Range and train indicator.

Working with the SG, the operator is concerned primarily with the range and train indicator unit from which he can control the entire radar gear. A close-up of this unit is shown in figure 4-SG-1.

All the controls on the range and train indicator may be divided into three groups: power, operating, and pre-set. All the power controls are grouped on the left and extend from top to bottom of the unit, except for the dial lights switch, which is at the far right of the pre-set group. The second group, operating controls, extend along the center of the panel. The third group is the bottom row of pre-set controls.

Identification and function.

It is important to be able to identify, and to know the functions of all of the controls. For ease in locating and identifying, all controls in figure 4 SG-1 are either numbered or lettered.

2. Meter B is identical to one located on the transmitter-receiver unit, and indicates line voltage. This meter should read between 110 and 120 volts AC. If it does not, call the maintenance man.

3. The other meter, C, indicates transmitter current when switch K is in NORMAL position. Transmitter current as indicated on meter C is controlled by the setting of the variac (E). The variac should be set so that the transmitter current reading on meter C is between 15 and 25 milliamperes. If this reading cannot be attained, notify the maintenance man. With Switch K in MONITOR or RECEIVER TUNE position, meter C duplicates respectively RF. monitor and tuning indicator meter readings at the transmitter and receiver

4. The radiation switch D controls intermittent and continuous operation of the transmitter. For intermittent operation, switch D must be held in KEY position, as there is a spring action that automatically returns the switch to OFF position. LOCK position is for continuous operation.

5. Variac (E) controls the power supplied to the transmitter.

6. The scope (F) is the range scope. Ranges are read directly on the range counters (G). A modified method for quick and approximate readings is to place a calibrated scotch tape scale on the "A" scope below the sweep. The same can be done at the PPI (I) by drawing with india ink 5,000-yard circles for the 15,000-yard range; then, on the 75,000-yard range, these circles will be 25.000 yards apart.

7-8. Bearing is read on indicator H and PPI (I). True bearing is read from the outer scale, while relative bearing is read from the inner dial, when synchro switch (J) is in NORMAL position. If ship's gyrocompass repeater system should fail, switch J must be thrown to EMERGENCY for equipment to operate, giving relative beatings only on the outer dial.

9. When the radar is operating, switch K is in the NORMAL position. The other positions, RECEIVER TUNE and MONITOR, are for purposes stated in 3 above.

10. Receiver sensitivity is controlled remotely by the operator through receiver gain control (L).

11. Receiver's tuning is controlled remotely by the operator with receiver tune control (M) This is set for maximum return signals.

12. The range crank (N) is geared to the range counters and also moves the step in the time

13. There are two range scales. 15,000 yards and 75,000 yards. Switch P permits the operator to select either of the two ranges.

14. Switch Q allows the operator to receive either signals or range markers on the range scope and PPI. Normally this switch is on SIGNALS. In order to insure that the gear will give accurate ranges, the operator must cheek frequently (at least once each watch) the range calibration by switching range markers to the scope. This procedure is described later, in the section on Calibration.

15. The antenna's rotation may be controlled either manually or automatically by switch R. From its center position moving switch R to right gives automatic clockwise rotation; moving it to left gives automatic counterclockwise rotation. There are four positions for four speeds on either side of center.

16. Remote range switch (T) and remote bearing switch (U) permit transmission of ranges and bearings, respectively, to range and bearing indicators located on the bridge, gun control, torpedo control, and plotting rooms. At these stations there are selector switches for cutting in either range and/or bearing indicators. As a rule, remote range and bearing are always in the ON position at the range and train indicator and OFF at the selector switches when bearings or ranges are not desired.

17. As a safety precaution against overloading the transmitter, there is a relay which trips during any overload condition. This relay can be reset by the operator by pushing reset button (V).

18. Switch W will determine the positions OFF, INTERMITTENT, and CONTINUOUS operation for IFF equipment when it is installed,

19. Switch X adjusts the IFF gain.

20. Range focus (1), permits the operator to adjust the sweep on the range scope, permitting a sharp, even trace for the entire width of the scope. This setting is made on installing a new tube.

21. 15,000-yard zero set (2) adjusts the calibration for the lower end of this range scale.

23. 75,000-yard zero set (4) adjusts the calibration for the lower end of this range scale.

24. 75,000-yard limit set (5) adjusts the calibration for the upper end of this range scale.

25. Pulse frequency (6) controls the pulse repetition frequency. There are three adjustments, A, B, and C, which are used to reduce interference from other radars of approximately the same frequency. The control (6) is set on the letter giving the minimum interference. This control also is used for identifying second-sweep echoes. More will he said about this in the technique section.

26. PPI focus (7) permits the operator to adjust the sweep on the PPI for a sharp, even trace.

27. Dial lights switch (8) controls the intensity of lights on the PPI, bearing dial, and counters. Pilot lights switch (9) controls light intensity for the red and amber lights opposite the stand-by and radiation switches (this control has been omitted on later models).

28. There are five screwdriver adjustments with which the operator should not tamper once the set is operating normally.

29. There are two fuses with which the operator should he familiar. These fuses are located on the front panel near the transmitter current meter (C). One is marked INDICATOR F-902 (10), and the other is marked BEARING CONTROL F-901 (11). If, for any reason, the antenna or indicator should stop functioning, the operator should check these fuses before sending for the maintenance man There is a further description of these fuses in the section on Operational Technique. So far the controls on the range and train indicator unit have been identified. The operator should become so familiar with these controls

TURNING ON AND OFF

Turning on.

Let us assume that the transmitter and receiver unit are ready for operation. When starting the gear for the first time, check to see that the controls are set as follows:

Steps 1 through 8 represent the normal settings of the range and train indicator unit when equipment is on STANDBY, and from which the SG can be placed in operation as follows:

Turning off.

In order to shut down the equipment the above procedure should be reversed.

CALIBRATION

Calibration of the range counters.

To make sure that the equipment will give accurate range readings, the operator should check the calibration of the range counters at least once every watch (every four hours). To do this, the range selector switch (P) is first set to the 15.000-yard position and the signal-markers switch (Q) to the MARKERS position. Markers representing divisions of 5,000 yards

The operator also checks the counters on the 75,000-yard range scale, Then, if the selector switch is in the 75,000-yard position, a series of markers will appear on the time base, each representing distances of 5,000 yards. The appearance of these markers will vary somewhat on different installations, and this difference must be clearly understood if the calibration is to he done correctly. The zero marker may or may not

The step is first lined up with the center of the 5,000-yard marker, and the range counters should read exactly 5,000 yards. Next, the step is cranked until the 75,000-yard marker begins to drop down. The counters should read exactly 75,000 yards. The 75,000-yard marker will be the sixteenth or fifteenth, depending on whether the zero marker is, or is not visible.

If the calibration of the range counters is not correct, the operator will perform the following operations:

External calibration.

It is important that the external calibration of the set he checked periodically. This may be done by using one of three methods. It may be determined

Be sure the set has been warmed up and calibrated carefully before trying to determine its error. When determined, the error can be compensated in calibration. Thus, to compensate for the error in the above example, set the range dial to 5,200 yards, and 15,200 yards instead of 5,000 yards and 15,000 yards,-line up the first and third range marks with the step as before. Now all ranges read on the 15,000-yard scale will he 200 yards higher and therefore correct. Make the same compensation on 75,000-yard scale.

OPERATIONAL TECHNIQUE

Tuning the receiver.

The operator has only one tuning control to adjust. This control is the knob marked receiver-tune (M) located next to the range crank.

When the set is turned on from the stand-by condition, it takes about twenty minutes for the oscillator frequency to become stable. The tuning will have to be adjusted frequently if the set is to be used during this first 20 minutes. After this "warm-up" time the tuning will be fairly stable, but should be checked at least every half hour, or by each new operator. Experience will indicate how often your particular set must he tuned. Some sets require more frequent tuning than others.

The following procedures are used to tune the receiver:

Land echo. The best method is to tune on a land echo. Stop the antenna in order to get a good steady land echo on the "A" scope. Turn the gain down to where the echo is not saturated (to where it is about half of its maximum height). Then adjust the receiver-tune control (M) until the signal is at its maximum height. The technique for determining maximum signal height is to turn the tuning control rapidly when approaching the maximum height, going a little beyond and a little under maximum signal, and

Ship echo. The next method is similar to the foregoing but is not so effective. Tune on an echo from another ship. The same procedure is used; however, trouble will be experienced because the echo will bounce up and down. Tuning on an echo of this type requires a certain amount of skill and experience.

Sea-return. Another method, which, under certain conditions such as especially heavy weather is better than tuning on ship echoes, is to tune for maximum sea-return.

The sea-return consists of many bouncing echoes which extend out, sometimes as far as 6,000 yards. The operator should operate the set on the short-range scale, watch the "A" scope, and tune for the point where overall sea-return is highest and extends out to the greatest range. An illustration of how sea-return should appear is shown in figure 4 SG-3.

Meter. If there are no echoes or sea-return available for tuning, throw the receiver tune-normal-monitor switch (M) to the RECEIVER TUNE position. Then tune for the highest reading on the transmitter current meter (C), using the receiver tune (M) control. Do not fail to return switch to NORMAL after tuning, since in receiver tune position, ranges will be 500 yards off.

Fig. 4 SG-3. Sea-return on the "A" scope using 15,000 yard range scale.

Long-range search or large target search.

The "A" scope will show targets at greater ranges than the PPI; therefore, it is necessary that the "A" scope he used in the long-range search. The PPI is, however, much easier to watch, and once a target appears on it, there will he little chance of the operator missing the echo.

Because of the above considerations, a long-range

Switch to the 75,000-yard scale and adjust the receiver gain for about 3/8-inch of grass on the "A" scope. Then, for approximately five minutes, search with the antenna on automatic rotation at the slowest speed. The operator should watch the PPI for two antenna sweeps, then the "A" scope for two sweeps, then the PPI for two more, and so on for the rest of the five minutes. At the end of this time, switch to hand rotation and make a slow hand rotation of a full 360 degrees, watching the "A" scope very carefully. After this, repeat the automatic rotation search.

The speed used for automatic rotation is 4 rpm in the first position. Some ships have changed this so that the first position now has an antenna rotation speed of 1 or 2 rpm. If the set aboard your ship does not have a rotation as slow as this, the technician can easily change it to the desired speed. When this adjustment has been made, the operator can use the second speed of rotation, 4 rpm, for normal search, and lie can use the first speed in place of the hand search.

Close-range search or small target search.

This type of search is primarily intended to detect surfaced submarines, periscopes, or PT boats, although it has other functions. The following procedure should he used.

Switch the range to the 15,000-yard scale. The search is conducted by watching the PPI scope, using an antenna speed of 1 or 2 rpm, (or 4 rpm if that is the slowest available).

Two conditions requiring special attention are likely to be encountered in this type of search. The first is sea-return, which may extend to 1,000 or 2,000 yards, and in rough weather to 6,000 yards. With the receiver gain up to its normal value, targets at close range will be hidden in this sea-return. To detect, or to get bearings and ranges on targets under these conditions, it is necessary to reduce receiver gain. It should be borne in mind, however, that the gain is reduced only when checking these close targets, and then only for a very short time, since the gain must be up if the small echoes from submarines are to be detected.

The other thing requiring consideration on this range is the saturated echo. Targets at such short ranges give strong echoes. On the "A" scope these echoes are saturated; that is, they have flat tops. To get an accurate range on this type echo, the range dial should be cranked to a point at which one-half of the

To get an accurate bearing on these strong echoes, the PPI should be used. Rapidly rotate the antenna back and forth so that the entire echo is visible on the PPI; then quickly stop the antenna so as to bisect the echo.

Station keeping.

For station keeping, it is not usually necessary to obtain extremely accurate ranges and bearings. In normal steaming, ranges and bearings to the guide ship may he obtained with sufficient accuracy for keeping station without stopping the antenna rotation. The PPI scope is used to approximate the bearing. The bearing is read off the scale surrounding the PPI by mentally drawing a line from the PPI center through the target to the scale. The range may be approximated by several different methods. The best method is to mark permanent 5,000-yard circles on the PPI with India ink-, and to estimate range in relation to these. A second method is to switch the signal-markers switch to MARKERS. As the antenna rotates, 5,000-yard circles will remain for a few seconds after the switch is turned back to SIGNALS. The range to the target may be estimated by noting its position relative to the marker circles. The third method is to put a piece of scotch tape on the "A" scope and ink a scale of ranges on it. Then, as the antenna sweeps by the target, the operator watches for the pip to jump up on the range scope and obtains the range from the scotch tape. A new rotating scale device is being placed on the PPI's of many of the SC's in the Elect. The range and bearing of target

The above-mentioned methods of approximations are usually satisfactory for normal station keeping. While taking a new station, or during formation changes, it will usually be necessary to get accurate ranges and bearings in the normal way.

Radar was not meant to supersede regular station keeping methods. Since such use cuts down the search efficiency, employment of radar for station keeping should be kept to the absolute minimum.

Auxiliary fire control.

The SG may he called upon for fire-control work, especially torpedo fire-control on destroyers. There is always the possibility that the fire-control radars may be put out of commission, making it necessary to use the SG to obtain accurate bearings and ranges to be used in the computers. This can best be done by stopping the antenna. However, since such procedure cuts down the efficiency of the search, tracking should be carried on without stopping the antenna unless accuracy is absolutely vital. It is recommended that at least one 360 degree sweep be made per minute while tracking, to guard against surprise.

Shell splashes can be picked up when the antenna is trained in the direction of fire. On the "A" scope the echo will jump up rapidly, and a quick estimation of range difference between it aid the target echo may he made. If the antenna is rapidly rotated back and forth by hand so as to cover a small sector near the target, the splashes may appear on the PPI. It is

Navigation.

The SG is extremely useful to the navigator, particularly when operating in close waters. The navigator who is always cognizant of the ship's position will he able to give the operator the approximate bearing, distance, and expected time of contact with land. From his chart lie will be able to tell if the land rises abruptly out of the water, or, in case the land is low lying near the beach, whether or not it rises farther inland.

Land that rises at the water's edge to considerable height is excellent for radar purposes since the closest land appearing on the PPI in this case, is usually the beach. The chart should always be checked for the possibility of inland mountains appearing; first, by checking the altitude of mountain peaks against the altitude of the shore line, and second, by checking the outline of the shore from the chart against the outline from the PPI. In eases of this type of land, the outlines will be almost identical, and comparison with the chart may be used to fix the ship's position. Almost all the islands in the Aleutians are of this type.

Another type of situation involves a low-lying shore line and inland mountains. When contact is first made, only the mountains will appear on the PPI, since the low shore will be below the horizon. With this type of land it would be a dangerous mistake to assume that the beach is the closest contact. Failure to remember this may result in the ship's grounding. For this same reason, unless your knowledge of the contour of the land justifies it, never depend on bearing tangents for fixing your position.

The best fixes are not necessarily obtained from a large group of random ranges and bearings, or from the closest land. The best method is to obtain a few accurate ranges and bearings of small prominent objects. Isolated rocks, small distinct islands, and isolated mountain peaks are excellent for obtaining fixes. The prominent points may be chosen from the chart. If the ranges and bearings obtained on two or three of them plot in at the same point, it is safe to assume that that point is your position.

Always remember to make use of the contours of the land when employing radar for navigation. By closely examining the echo of the "A" scope for multiple peaks and other peculiarities, the echo may be more definitely fixed to some position on the chart.

Islands in the mid-Pacific are very flat, and rise only a few feet above sea level. These islands are usually

Sometimes it is possible to detect shoals on the radar screens, if the shoals are close enough to the surface to cause a disturbance in the water. The signal appearing on the radar screen would be much the same as a "wake" signal obtained from another ship. However, shoals are very treacherous and ships should not rely upon radar to detect them.

Composition.

When a contact is detected on the SG, it is extremely important that certain facts be determined about its composition. Ability to obtain these facts comes largely from experience, but the following hints may be of value.

Type and number of ships. The range of initial contact is the best indication of target size. Fixed antenna height results in ships of a certain size usually having a certain maximum range. Thus, on a ship where it is usual to contact battleships at 40,000 yards and destroyers at 25,000 yards, first contact at 38,000 yards would indicate a ship of battleship size.

Echoes from large ships will he much steadier than those from small ships, and will usually appear thicker on the "A" scope. On first contact or at great distance, the "A" scope should be used for determining the number of ships in a contacted group. Turn the receiver gain down, and examine the top of the echo for multiple peaks, counting as many as possible. It should be remembered that when contact is first made, only the large ships will appear, since the smaller ones will still be out of range.

Aircraft. Pips from aircraft will appear quite erratic, the echo fluctuating rapidly on the "A" scope. On the PPI they are apt to appear very strongly on the antenna sweep, be absent on the next sweep, and appear at some other position on the next sweep. They may be recognized by their fluctuating echo and rapid change of position.

Land. Land echoes are steady and are likely to be quite wide. When plotted on the DRT, their position will remain stationary.

False echoes. Various types of false echoes are encountered with the SG. They are not caused by trouble in the equipment, and are not truly false for they are actually caused by some reflecting surface. They are, however, considered false because they indicate objects in which we are not interested.

In close formations, double-range echoes are quite common. They are caused by the returning echo reflecting off the searching ship, again reflecting off the target, and finally reaching the antenna. This type of false echo may be recognized by three factors; first, it will always be at the same bearing as one of the large targets; second, it will be at exactly twice the range of the large targets; and third, it will vary rapidly in amplitude.

Second-sweep echoes result from long-range echoes arriving back after the next sweep has started. With a pulse rate of 1,000 c.p.s., there is time for 81 miles of range between each pulse and sweep. Thus, for an echo to appear on the second sweep it must be over

Another type of false echo results from reflection off some part of the ships structure. These echoes occur when the mast or superstructure is in the path of the radiated beam. The energy reflects off the interfering structure, hits the target, and returns by the same route. The false echo will be at the same range as some real target and on the bearing of the

PPI echoes. When cruising in close formation with other ships, the picture that appears on the PPI will give the impression that we can determine the course of each individual ship simply by observing the PPI. This is definitely not true; although all the ships are on a similar course, each appears on the PPI to be on a different one because of the curved pip resulting from the radial sweep.

Jamming and deception.

There is no doubt that the enemy considers our radar an extremely dangerous weapon, and consequently it is only reasonable to expect him to try every means possible to make it less effective. He may use two tactics to do this: jamming and/or deception. Every operator should learn how to recognize these countermeasures, and expect them when in combat zones.

When the enemy broadcasts radio signals intending that our radar receive them, and they show a confusing pattern on the screen, it is called jamming. Use of dummy targets (tinfoil, kites, balloons, etc.) is called deception. More precise definitions are sometimes given, but these are satisfactory for this discussion.

The SG radar can be jammed, and it will show echoes from the tinfoil the enemy sometimes throws out to confuse the operator. The operator should not become alarmed when either of these things happen.

If you were suddenly confronted with jamming without previous experience, it would appear impossible to work through. However, it is not really that serious if the following procedure is carried out:

The first reason for obtaining a bearing on the jamming is to determine whether or not it could be accidental interference. Jamming will not only be directional, but its true bearing will not be changed by any sudden change in your ship's course. Interference originating aboard your own ship will either be non-directional and appear on all bearings, or else it will

Try moving the gain control up and down. This is probably one of the most important countermeasures that can be taken, and the one most commonly overlooked because of its simplicity.

In most cases, except when effective noise modulated jamming is being encountered, there is a setting of the gain control with which it is possible to range on a target in the presence of heavy jamming. If there are several echoes on the same bearing, the best setting for each echo is different. Of course it is more difficult to obtain these ranges because of the distortion of the echo produced by jamming, but it is, after all, possible to obtain the desired information. The extra effort is worth while because the enemy would not be jamming unless he were trying to conceal something important.

Two general methods of using the gain control, both of which should be tried, are as follows:

Try changing receiver local oscillator tuning. When you change the rec. tune, you lose some of the height of the desired echo. However, if the jammer is not exactly on your radar frequency, there is a chance that you will detune the jamming signal more than the echo signal. Considerable improvement can sometimes be obtained in this way. Try "swinging" the rec. tune dial in both directions to see which direction brings the greatest improvement. Note the correct setting of the rec. tune dial so that it can be returned to its normal position when no jam is present, or if detuning does not help.

Keep operating. Even if the jamming is extremely effective, keep trying and do not turn your radar off. Turning your radar off informs the enemy that his jamming is effective, and certainly makes the radar completely worthless. The effectiveness of the jamming may change from time to time, so if you are persistent enough some information may be obtainable.

Report the nature and bearing of jamming to CIC. Recognizing the type may be difficult because nonsynchronous patterns sometimes appear blurred beyond recognition. Inasmuch as knowledge of jamming type ^* may possibly help identify the jammer

Above all, never turn off the radar.

When jamming and/or deception is encountered, full 360 degree search must be continued. However, the antenna should be stopped for short intervals from time to time, in order to try reading through the jamming (using the "A" scope). You also must be prepared for any diversionary tactics, for the enemy may or may not use jamming and/or deception to divert your attention from the bearing of the main attacking forces. This problem is simplified somewhat when similar but separate radars are used for reading through jamming and for searching.

PERFORMANCE

Maximum reliable range.

Ranges in surface craft obtained with the SG are dependent on the antenna height. Expected ranges with a typical antenna height should he of value to the new operator.

The results listed below are maximum reliable ranges for a 90-foot antenna.

Range accuracy is +/- 150 yards.

Bearing accuracy is +/- 1 degree.

Resolution.

Assuming two targets to be on the same bearing, the SG can distinguish between them at short ranges when they are separated by no more than 300 yards; at longer ranges approximately 500 yards separation is needed. At any range, too high gain tends to cause the pips to merge, and reduces discriminatory power. In general, the SG is able to discriminate in range between two targets separated by 300 yards or more on the "A" scope, and 500 yards on the PPI.

With respect to bearing, a comparable minimum limit exists and is expressed in angular rather than linear measurement. Since the transmitted beam does not travel along a single line, but has an angular spread, it can be seen that if there are two targets at the same range, one in the center of the beam pattern and the other in the edge, an echo will be returned from the target in the center and from the target in the edge, and these will appear as one echo. By reducing receiver gain it will often be possible to distinguish both targets. At normal ranges the angular separation necessary for target discrimination in bearing is 5 degrees using the "A" scope, and 9 degrees using the PPI.

TROUBLES

Major troubles are handled by the technicians but time will be saved if the operator is able to recognize some of the minor breakdowns.

If the sweep traces on the "A" and PPI scopes suddenly go out, the indicator fuse next to the "A" scope should be checked,

If the red light goes out, sweeps disappear, and the plate current drops to zero, the overload relay probably has kicked out. Torn the high-voltage variac all the way down, press the overload reset, wait for the red light to come on, and then turn up the variac to the proper value.

When ranges appear to be 500 yards too high, the receiver-tune- normal monitor switch should be checked to see if it is on NORMAL position.

If the sweeps on either scope appear fuzzy, their respective focus controls should be adjusted.

There are certain occurrences which are entirely normal on the SG but which might be interpreted as troubles by the new operator.

If the synchro excitation to the antenna control motor should fail, the operator will be able to detect the trouble almost immediately. When the synchro supply goes out, the antenna will stop rotating, even though the "bug" continues to rotate and the sweep continues on the PPI. However, the picture on the "A" scope will stay constant because the antenna is not rotating, and the picture on the PPI will appear

If the synchro excitation should fail while at sea, and there are no targets on the screen, it will be difficult to detect what is wrong. The operator might detect the trouble by close observation of the "A" scope for changes in sea-return signals. If there seem to be no changes in the signals the operator should have someone cheek visually to see if the antenna is rotating.

Sometimes targets will be obscured by radar interference. This appears as either a series of dots, or as a series of radial lines on the PPI. There is not much that can be done to correct the situation: however, changing the pulse rate sometimes changes the interference pattern so as to make it less objectionable. When interference is severe, use the "A" scope.

SC-SK RADAR

The SC-2 radar is similar to the SC-1, but incorporates a few modifications. The sweep circuit has been revised, and the antenna has been re-designed, with a directional IFF antenna included. A PPI unit has also been added. The SK radar at present is an SC-2 with an antenna four times as large. The SC-2 or SK radars are composed of six units, as follows:

The operator is concerned principally with the first two units, and possibly with the fourth, and the duplexer unit of the sixth. Ordinarily, the technician tunes the transmitter, preamplifier, duplexer, and receiver. The operator checks the tuning of the receiver at the beginning of his watch.

CONTROLS

Control unit.

A. Main power switch: controls power to all units.

B. Transmitter-plate voltage: this switch, when snapped on, applies all power to the transmitter. As it is turned clockwise, it increases the high voltage applied to the transmitter tubes.

C. Relative-true bearing switch: when on TRUE the antenna is controlled by the ship's gyro system. Relative bearings are read on the outer dial, and true bearings on the inner dial of bearing indicator (M). When on RELATIVE, the antenna is controlled by power from the set. This maintains antenna control in the event that gyro power fails. Only relative bearings to the outer dial may then be read.

E. Remote bearing mark: buzzer or horn switch to notify remote station when readings may be taken.

F. Automatic-manual toggle switch: power switch to slewing motor, which gives automatic antenna rotation.

G. Antenna-control switch: center position is off. Right gives clockwise rotation. Left gives counterclockwise rotation. Speed is controlled by the amount of turning.

H. Hand crank: for antenna control.

J. BL power switch; may or may not be used.

K. Sweep: local-PH; PPI position used when in sector search. Local position is the normal operating position.

L. Overload relay reset.

M. Bearing indicator: inner dial-true; outer dial-relative.

N. Brightness control of bearing indicator light.

P. Brightness control of pilot lights.

Q. Transmitter pilot light.

R. BL power pilot light.

Receiver unit.

AA. Radio frequency tuning control.

XX. Local oscillator tuning control.

BB. Receiver gain control.

Indicator unit.

CC. Receive-calibrate switch.

EE. Brilliance control: controls brightness of the trace.

FF. Focus control: controls width of the trace.

GG. Astigmatism control: controls uniformity of focus along length of the sweep.

HH. IFF gain control.

JJ. Calibrate maximum.

KK. Calibrate frequency.

LL. Calibrate minimum.

MM. Challenge switch for IFF: puts the IFF system into operation from standby.

NN. Synchronizing switch: EXTERNAL-INTELNAL: normal operating position on EXTERNAL. Brings synchronizing pulse from transmitter to the indicator. INTERNAL position may be used for adjusting sweep and calibrating frequency when high voltage has not been turned up.

PP. Crystal switch.

QQ. Range step height control.

SS. Vertical trace centering control.

TT. Range crank.

UU. Horizontal sweep centering control.

VV. Synchronizing pulse gain control.

WW. Range selector switch:

ZZ. Power switch for receiver indicator unit.

PPI unit.

1. Mark-IFF switch: normal operating position on IFF. When on MARK, range step is shown on PPI.

2. Dimmer control for PPI bearing dial light.

3. PPI power switch.

4. Brilliance control.

5. Bearing indicator switch; RADAR-PPI: when on RADAR, bug follows the antenna; when on PPI, bug follows the yoke (cursor).

6. Focus control. 7. Bearing indicator adjustment control: for synchronizing bug reading and cursor reading, when operating bearing indicator switch is in the PPI position. Depress knob and set cursor (bearing blade) to read with the bug, then release knob to again engage the cursor.

8. Sector search control: in normal position, which is DOWN, clockwise rotation of the control increases the sector. Counterclockwise rotation narrows the sector. When pulled UP to engage the cursor, the sector may be rotated by rotating the cursor.

9. Sector search off-on switch.

10. Remote alarm button.

11. Relative-true switch for PPI.

12. Calibration control.

13. Range selector switch:

14. Centering control: controls only centering of sweep along axis of sweep.

Preamplifier unit.

1. All controls on the preamplifier unit are tuning controls.

TURNING ON AND OFF

Turning on.

1. Turn the main power switch (A) ON. The dial light of the bearing indicator will light, and the amplidyne motor will start,

2. Turn the transmitter plate voltage variac to 10. The pilot light (R) will light up and the filaments in the transmitter oscillator and power supply will glow.

4. Turn ON the power switch of the PPI unit. The lamp for the bearing glass will light.

5. After waiting a half minute, the filaments of the transmitter tubes will be hot, and the plate voltage variac (B) should be turned slowly up to between 70 and 100. This value is determined by the technician.

6. Turn on BL power switch (J).

7. Start the antenna rotating by setting switch (F) on AUTOMATIC, and switch (G) to give a slow rotation of the antenna.

8. Turn up PPI intensity control (4) until a trace appears.

9. Adjust focus (6) to get fine uniform trace.

10. Center sweep with control (14). This adjustment should be made so that the beginning of the sweep starts at the same point regardless of the bearing. That is, there is no overlap of the sweep and no open portion. If the center of the sweep is not at the center of the scope, the technician must make internal adjustments.

Turning off.

1. Turn down (CCW) PPI intensity control (4).
2. Turn off power switch for PPI unit.
3. Turn off BL power switch (J).
4. Turn off automatic switch (F).
5. Turn switch G to OFF position.
6. Turn off receiver indicator power switch (ZZ).
7. Tarn plate voltage variac fully CCW.
8. Turn off main power switch (A).

CALIBRATION

Calibrating the range scope.

1. Turn switch (CC) to CALIBRATE.

2. Turn switch (WW) to Range 1.

3. Adjust brilliance (FE), focus (FF), and astigmatism (GG) for a fine uniform trace. These controls interact one on the other, and must he adjusted together.

4. Turn crystal switch (PP) to ON. A "figure of eight" with the lower half clipped will now he observed on the "A" scope. If this figure is not observed:

5. Release lock and adjust (KK)-frequency

6. Turn crystal switch (PP) to OFF.

7. Crank (TT) so that 2,000 yards is observed on the first range counter.

Figure 4 SC/SK-3. Figure of eight determines when calibration pips are 2,000 yards apart.

8. Release lock on calibrate minimum (LL) and adjust position of range step with (LL) so that the top of the second marker just begins to drop. (See fig. 4 SC/SK-4.)

9. Crank (TT) so that counter reads 20,000 yards.

10. Release lock and adjust calibrate maximum (JJ) so that the top of the eleventh marker begins to drop.

11. Check the 2,000-yard setting and if it has changed, repeat step 9.

12. Check the 20,000-yard setting. If either (JJ) or (LL) is changed, it affects the other. Keep checking until no further adjustment is necessary; lock both controls.

a. To make the calibration and ranging uniform on SC-2 and SG, the center of the range mark and the center of the target pip are used.

b. It is easier to range on the center of a pip than on the leading edge.

c. This introduction of error compensates for a range error on SC radars when calibrated against fire-control radar.

Calibrating the PPI.

The PPI unit must never be calibrated until the "A" scope has been calibrated, since it is dependent on the accuracy of the calibration of the "A" scope.

1. Turn the mark-IFF switch (1) to MARK.

2. Set the range selector (WW) to Range 2, and set the counter to 60 miles.

3. Set the PPI range selector (13) to Range 2.

4. With the antenna rotating rapidly, a circle will appear on the PPI scope. Set calibrate control (12) so that the inboard edge of the trace corresponds with the 60-mile ring on the scope face.

5. Set the range counter to 30 miles and check the calibration. If the internal calibration of the set is correct, the PPI will be calibrated for all three range scales.

With the orange filter glass on the PPI, the range marks are so far from the screen that errors of several miles in range are possible because of parallax. The authorized revision should be made, whereby the filter glass is removed and the range lines made directly on the face of the PPI scope. This is (lone with a drafting compass and India ink as outlined below.

Direct reading of the PPI on the 75-mile range scale is now easy and accurate. The solid circles are 15 miles apart. The dashed circles are 5 miles apart. The range of any indication may he read accurately to the nearest mile. Bearings are read by bisecting the indication with the cursor, and reading the bearing on the illuminated indicator.

OPERATIONAL TECHNIQUE

Tuning the receiver.

The technician will have the transmitter tuned for maximum power output and it should not be touched by the operators.

The preamplifier and receiver are also tuned by the technician, and only slight adjustments need he made by the operator. Care should be taken when tuning on a bobbing echo that increase in echo height results from tuning adjustments and not from bobbing of the echo. Tune for maximum results from tuning adjustments and not from bobbing of the echo. Tune for maximum echo height by going a little over and then a little under maximum. Jockey back and forth rapidly, and stop between the two points, a little over and a little under, for optimum tuning. If land echoes are available, they should be used for tuning. In any event, all operators should know the dial settings of the receiver for maximum echo height.

Long-range search.

Long-range search, so called, is essentially search for initial contacts at any range. It will he conducted either when there are no indications on the screen at

The range scale used on the scopes will depend on the tactical situation. In a carrier task force, initial contact at the longest range is highly desirable. Two methods of search are possible:

When using the first method, most careful watch is made on the PPI scope with occasional search on the "A" scope. As the PPI is the less tiring scope to observe, most operators prefer this method.

The alternate method employs the closer watch of the "A" scope with occasional search on the PPI scope. The advantage of this method is that if a contact is made within 75 miles, tracking may be begun immediately on the PPI without changing scale.

If the task force has no air support, 75-mile warning of approaching aircraft is sufficient, and both scopes may be operated on the 75-mile range.

The receiver gain setting should he such as to give approximately 3/8-inch of grass on the range scope when the operator is giving his attention to the PPI scope. This should he reduced to between 1/16- and 1/8-inch when attention is given to the range scope.

The antenna should he rotated at a rate of approximately 1 1/2 revolutions per minute. A plot should be started on the first indication no matter how weak the signal. On the next sweep of the antenna, it may be stopped, the blip on the range scope studied to determine composition, and the plane challenged with IFF equipment. Normally this pause in continuous rotation should not take more than 15 seconds,

Searching over land.

If search must be made over land, target pips will be mixed with the land pips. However, planes will give echoes which bob up and down more rapidly and irregularly than the land pips. Also, the plane pip will move with respect to the land pips. When faced with the problem of searching over land, the antenna may he stopped for a few seconds to determine whether the pip is actually behaving as a plane echo or as a land echo. Bearings cannot be obtained very accurately, but the bearing of maximum swing of the

The operator must remember to keep searching. He should not find one target and "camp on it" from then on.

Multiple-target tracking.

Multiple-target tracking should be done exclusively on the PPI. In the large majority of cases, the 75-mile scale is the proper scale for multiple-target tracking. Rapid ranges and bearings may be accurately obtained on targets at from 10 to 80 miles, and a good search for new targets at ranges up to 80 miles is maintained. The antenna rotation speed should be increased to 2 rpm, and half of the targets reported for each revolution. Gain setting should be for 3/8-inch of grass on the range scope. All ranges and bearings are read from the PP 1.

Fighter-director tracking.

To a good operator, there s no essential difference between multiple-target tracking and ID tracking. With the antenna rotating at 2 rpm, reports can be given on the intercept planes and bogies at 30-second intervals, by reporting these targets on every revolution of the antenna, if desired by the fighter director officer. A good track can be kept on all other targets by reporting them every other revolution, giving one minute reports to the plotter. Ranges and bearings should come directly from the PPI operating on the 75-mile range with the gain set for 3/8-inch of grass on the range scope.

It may happen in certain instances during night attacks, that the gunnery officer or assistant gunnery officer will want to man the PPI himself. He will then be in a position to direct AA fire rapidly, and the information will not be delayed by going through CIC and plotting.

Fire-control liaison.

Fire-control liaison may be conducted on the 75-mile range with normal gain setting at about ten miles, provided there are not many targets at the same range. With several targets on different bearings within ten miles, their echoes and side lobes will ring the PPI scope and cause too much confusion for fire-control coaching.

When the primary interest is fire-control coaching,

When the set is operating so as to read true bearings on the PPI, only true bearings are put on a repeater. If relative bearings are desired, the PPI relative-true switch can be thrown to RELATIVE, and the bearing indicator switch from RADAR to PPI. The bug is then adjusted to read the same on the outer dial as it is read on the yoke. Now, all bearings from the PPI will be relative, and the repeaters will read relative.

Composition.

Determination of composition of the target requires more operator experience and closer observation than any other phase of operation. Determination of composition involves use of IFF to determine whether a contact is friendly or not, and observation on both range and PPI scopes to determine number and size of planes in the group.

Large planes will have a low rate of fluctuation in echo amplitude, while small planes will have a high rate of fluctuation. The range scope is a better source of information on composition than the PPI scope. Upon making a contact, the antenna should he stopped on the target, the gain reduced to 1/16-inch grass on the "A" scope, and a thorough examination of the echo made. The number of planes can he estimated from the number of peaks on top of the echo. The range at which the target comes in is not conclusive proof of either its size or altitude, but is a major factor contributing to these estimations. The operator should give his estimate of the composition of every contact and this estimate should he substantiated or corrected by visual means whenever possible. The operator should then be notified of the exact number, size, formation, and altitude. Continuous repetition of this process is the only means of improving the operator's technique in determining composition.

Clouds, rain squalls, and ionized masses of air are readily detected on the "A" scope, and are usually easily disclosed on the PPI. Broad fuzzy pins, that

Any operator will learn to recognize land readily. However, most of them, on looking at a group of pips from land, will call the highest pip the highest peak of land as "seen" by the radars. This is wrong. The highest pip will be from that part of the land which has the best reflecting surface. The peak will be hard to identify if there is a range of mountains behind it, or mountains in the near vicinity at about the same range.

Jamming and deception.

There is no doubt that the enemy considers our radar an extremely dangerous weapon, and consequently it is only reasonable to expect him to try every means possible to make it less effective. He may use two tactics to do this: jamming and/or deception. Every operator should learn how to recognize these countermeasures, and expect them when in combat zones.

When the enemy broadcasts radio signals intending that our radar receive them, and they show a confusing pattern on the screen, it is called jamming. Use of dummy targets (tinfoil, kites, balloons, etc.) is called deception. More precise definitions are sometimes given, but these are satisfactory for this discussion.

The SC radar can be jammed, and it will show echoes from the tinfoil the enemy sometimes throws out to confuse the operator. The operator should not become alarmed when either of these things happen.

If you were suddenly confronted with jamming, without previous experience, it would appear impossible to work through. However, it is not really that serious if the following procedure is carried out:

The first reason for obtaining a hearing on the jamming is to determine whether or not it could be

Try moving the gain control up and down. This is probably one of the most important countermeasures that can he taken and the one most commonly overlooked because of its simplicity.

In most cases, except when effective noise modulated jamming is being encountered, there is a setting of the gain control with which it is possible to range on a target in the presence of heavy jamming. If there are several echoes on the same bearing, the best setting for each echo is different. Of course it is more difficult to obtain these ranges because of the distortion of the echo produced by jamming, but it is possible to obtain the desired information. The extra effort is worth while because the enemy would not be jamming unless he were trying to conceal something important.

Two general methods of using the gain control, both of which should be tried, are as follows:

Be sure to return the gain control to its normal setting when no jamming is present, or when the antenna is turned to an unjammed bearing.

Try changing receiver local oscillator tuning. When you change the oscillator tuning, you lose some of the height of the desired echo. However, if the jammer is not exactly on your radar frequency, there is a chance that you will detune the jamming signal more than the echo signal. Considerable improvement can sometimes be obtained this way. Try "swinging" the oscillator tuning dial in both directions to see which direction makes the greatest improvement. Note the correct setting of the oscillator dial so that it can he returned to its normal position when no jam is present, otherwise your radar will not give optimum results.

Even if the jamming is extremely effective, keep operating: do not turn your radar off. Turning your radar off informs the enemy that his jamming is effective, and makes the radar completely worthless. The effectiveness of the jamming may change from

Report the nature and bearing of the jamming to CIC. Recognizing the type may be difficult because non-synchronous patterns sometimes appear blurted beyond recognition. Inasmuch as knowledge of the jamming type* may possibly help identify the jammer in some cases, this information should be reported.

If the equipment is provided with an anti-jamming receiver, the jamming may he reduced sufficiently for reading targets without any detuning of the receiver. Detuning should be a last resort, and then should be done very carefully and cautiously, otherwise all targets may be lost and the equipment made completely ineffective. No set procedure is offered for setting the controls of the AJ receiver, except that they should be varied for maximum readability through jamming, the gain control coming first and then the AVC control followed by Rej 1 and Rej 2. Turn all AJ controls to the OFF or NORMAL position when no jamming is being encountered.

Above all, never turn off the radar.

Even when jamming and/or deception is encountered, full 360 degree search must be continued. However, the antenna should be stopped for short intervals from time to time in order to try reading through the jamming (using the "A" scope). You also must be prepared for diversionary tactics, for the enemy may or may not use jamming and or deception to divert your attention from the bearing of the main attacking forces. This problem is simplified when similar but separate radars are used for reading through jamming and for searching.

PERFORMANCE

Ranges obtained on planes will vary greatly with the altitude of the plane, because of fade areas and the curvature of the earth. Large, high-flying planes have been observed at 120 miles. Average ranges on medium altitude planes are from 60 to 70 miles, and on low-flying planes from 20 to 40 miles on the SC-1, with better results on SC-2 and SK.

Ranges on surface targets will vary with antenna height, size of target, and weather conditions. In most cases, the ranges will be 6,000 to 10,000 yards shorter than those obtained on the same targets with surface-search gear.

SC-2 RADAR

Antenna 90 feet

SK RADAR

Antenna 130 feet

Minimum range.

Accuracy.

Reading directly from the PPI, range accuracy is 2,000 yards or better, and bearing accuracy 4 degrees.

Bearing and range accuracies for the different ranges on the "A" scope and PPI, when the antenna is sweeping or stopped, are listed in the table below.

Resolution.

There are in general, two methods of improper operation. One will result in complete disappearance of all target indications from the screen. This should be observed by the operator instantly, and measures should be taken promptly to remedy the trouble. The other is a general decrease in the ranges obtained. Detection of this type of failure requires much greater alertness on the part of the operator.

The jar of gunfire or surge currents may cause the overload relay in the transmitter to kick out, cutting off the transmitter. The red transmitter pilot light will go out, all targets and the transmitter pulse will disappear from the screen, and the sweeps on the range and PPI scopes will be jittery, because they are not receiving a synchronizing pulse from the transmitter. The operator should turn down the high voltage variac, press the overload relay reset button, and then

A gradual decrease in the operating efficiency of a set is harder to detect. The operator must be on the lookout for this at all times. One indication may be the point to which the receiver gain control must be turned to get the normal amount of grass. The best indication is the ranges that are being obtained on objects with which the operator is familiar, such as ships in his group or land in the vicinity. If poor results are being obtained, the operator may try retuning the receiver. If this does not help, the maintenance man should be notified.

The operator can greatly assist the maintenance man by giving a true and accurate description of what happened on the scope when the set went our of operation. This is even more true of intermittent troubles.

MARK 3 AND MARK 4 RADAR
(FC, FD)

MARK 3 AND MARK 4 RADAR
(FC, FD)

Main unit.

1. Plate current meter of modulation generator: should read about 200.

2. Plate voltage meter of modulation generator: should read about 500.

Figure 4 Mk. 3/Mk. 4-1. Main unit.

4. Magnetron plate current meter: should he set, to read about 30 by controls 13 and 12.

5. Magnetron plate voltage meter: should be set to 12 (12,000 v.) by means of control No. 12.

6. Magnetron filament voltage meter: should read 13.5. Can be seen by looking through the wire mesh on the front of the transmitter.

7. Frequency control of modulation generator: adjusted by technician.

8. Radio dial light dimmer: controls the brightness of the illuminated dial on the receiver.

9. Receiver tuning control.

10. Receiver sensitivity control:

11. Load voltage control.

12. Magnetron plate voltage control.

13. Field control: adjusts plate current to the magnetron.

14. Remote-local switch: determines whether the receiver sensitivity is controlled from the main unit by control No. 10, or whether the sensitivity is controlled by the receiver sensitivity knob on the range scope.

15. Main off-on switch or line switch.

16. Plate off-on switch.

17. Dim-bright switch: controls brightness of the pilot lights on the face of the main unit.

18. Mon jack: used in tuning up the receiver.

19. Audio jack: used to obtain a synchronizing voltage when tuning up the receiver.

20. Screw lock for 21.

21. Magnetron filament voltage adjustment.

Control and indicator unit (range scope).

1. Intensity control: controls the brightness of the picture on the scope.

2. Image spread control: controls the size of the notch and expanded sweep.

3. Receiver sensitivity control: controls height of the grass and echoes.

4. Focus control: focuses the image on the face of the scope.

5. Sweep gain control: controls the length of the sweep. Should be completely clockwise.

7. Transmitter standby switch: turns the transmitter on or off. Used as a stand-by switch.

8. Pilot light dim-bright switch: (to be replaced by an A.G.C, switch.) Some sets have an anti-jamming switch above control 2.

Figure 4 Mk. 3/Mk. 4-2. Control and indicator unit.

Range unit.

1. Inner knurled nut: locks friction drive between the range knob, No. 3, and the electrical system controlling position of pips on the lace of the scope.

2. Outer knurled nut: moves images across the scope.

3. Range knob: moves images across the scope.

4. Pilot light bright-dim switch.

5. Dial light bright-dim control.

6. Signal button.

Train or elevation indicator.

1. Intensity control: controls the brightness of the image.

2. Image spacer control: move one sweep with relation to the other.

3. Sweep expansion control: opens or contracts the two steps.

Figure 4 Mk. 3/Mk. 4-4. Train or elevation indicator.

5. Pilot bright-dim switch.

TURNING ON AND OFF

Turning on the main unit.

1. Make sure main off-on switch (15) and plate off-on switch (16) are turned OFF and the plate voltage control (12) is turned completely counterclockwise (against the stop).

2. Turn on line transformer switch (mounted somewhere on the bulkhead).

3. Check magnetic controller switches (if any).

4. Turn on stand-by rotary switch near C and I Unit (when installed).

5. Turn on transmitter stand-by switch (7) on C and I Unit.

6. Turn on the main off-on switch (15). Before turning on anything else, listen to see if the blower fan cooling the magnetron starts running as soon as the main switch is thrown. The load voltage meter (3) should go to 120 volts. Adjust it to this value by means of the toad voltage control (it) and make sure it stays at this value. The plate voltage meter (2) in the modulation generator will swing to the right of the scale and slowly come down to about 500 volts. The plate current meter (1) on the modulation generator will start at zero and after a few seconds will slowly come up to about 200 milliamperes. When this meter reaches a stable value, the 1,639 c/s note will be heard coming from the modulation generator.

7. Turn on the plate off-on switch (16). Wait at least 5 minutes before turning up the plate voltage. When the plate switch is turned on, the two tubes located in the front of the high voltage rectifier light up.

8. After 5 minutes have elapsed, slowly turn up (clockwise) the plate voltage control (12) until the plate voltage meter (5) reads 12 kilovolts. Make sure the plate current meter (4) does not go above 30 milliamperes. Adjust the held control (13) until the plate current meter (4) reads 30 milliamperes (30 milliamperes is an average value, it will he different on some sets). The plate current and plate voltage are not independent. Any change affecting one will affect the other. Thus both plate voltage control (12) and held control (13) must be moved together.

9. Check filament voltage meter (6) to see if 13.5 volts are applied to the filament of the magnetron.

10. Check to see if the remote-local switch (14) is on REMOTE. The main unit is now turned on and the set is all ready to operate. It is a good policy to tune up the receiver upon turning on the set, and about once every hour thereafter-more frequently if the set is subjected to serious vibration or temperature change.

Turning off the main unit.

1. Turn the plate voltage control (12) counterclockwise slowly until it hits the stop.

2. Turn plate on-off switch (16) to OFF.

3. Turn main off-on switch (15) to OFF.

4. Turn bulkhead switches off.

When turning on any of the units in the director, the stand-by bulkhead switch, which turns on the scopes, must be turned ON-reverse procedure, for securing the gear.

Turning on the control and indicator (C&I) unit.

1. Turn sweep gain control (5) completely clockwise.

2. Turn intensity control (1) clockwise until an indication is observed on the face of the scope.

3. Focus the trace by means of the focus control (4). Note: For each setting of the intensity control there is a distinct setting of the focus control. Be careful not to make the trace too bright. The trace should never be so bright that the return trace can be seen over the notch. (This undesirable condition is apparent when the notch is fully expanded. It makes the notch look like a box.)

4. Turn the image spread control (2) completely counterclockwise.

6. Make your "zero set" and continue to check it as frequently as possible while operating the set.

7. Turn the transmitter switch (7) on. The instant this switch is turned on the set is "on the air." The main frame should never be turned off and the transmitter should be controlled by means of this switch; the switch is designed to do this, If it is found that fuses are blown by doing this, it is an indication that some element is not functioning properly and should be promptly remedied.

8. The lobing motor should he turned on only when using the set. It should remain on while searching for targets and while tracking. But remember, whenever the set is not actually being used, turn the lobing motor off.

Turning off the control and indicator unit.

1. Turn off lobing motor (6).

2. Turn off transmitter (7).

3. Turn intensity control completely counterclockwise (1).

Turning on the trainer's and pointer's scopes.

1. Turn the image spacer control (2) completely clockwise.

2. Turn the sweep expansion control (3) completely clockwise.

3. Make sure the range scope operator has the lobing motor turned on.

4. Turn the intensity control (1) clockwise until two horizontal lines appear on the scope. These lines will not be straight, but will be slightly curved.

5. Focus the traces by means of the focus control (4). It is important that the sweep should be just bright enough to see and no brighter. It should be focused to a fine, sharp line.

6. The image spacer (2) and the sweep expansion controls (3) should now be turned counterclockwise until the sweeps are about 1/4 inch wide and separated by about 1/8 inch.

Turning off the trainer's and pointer's scopes.

1. Turn the intensity control (1) completely counterclockwise.

Tuning the receiver.

1. Connect a patch cord to the vertical input terminals of the test scope. The BLACK side is

2. Connect another patch cord to the sync terminals. Connect the BLACK to the ground terminal and the RED to the high terminal. Sometimes the red and black markers have become obliterated. They can be readily distinguished, since the BLACK side, or ground side, is the outer conductor of the cable and probably will have no insulation on it. The RED side, or high side, is the inner conductor and will be insulated. This cable is plugged into the audio jack (19) in the modulation generator panel.

3. Turn the vertical and horizontal centering controls on the test scope to mid-position. Turn vertical amplifier knob off. Turn the horizontal amplifier knob to EXT. Turn the vertical and horizontal gain controls to zero. Turn the range to 550-4,500 (for RCA 155 A or B) or 700-7,000 (for RCA 155 C). Turn the frequency to zero. Turn the sync knob to zero.

4. Plug in the scope to 110 volts AC and turn the intensity clockwise until a click is heard.

5. Wait for about one minute and then turn the intensity control clockwise until a spot is observed on the screen. Be careful that this spot does not become bright. Turn the horizontal gain control clockwise until a horizontal line covers the scope with a small margin left over at each side. Focus this line by means of the focus control. Adjust the horizontal and vertical centering controls until one line is centered on the face of the scope.

6. Turn the vertical amplifier to the ON position. Increase the vertical gain control until the pattern occupies about 10 divisions on the scope.

7. Turn the frequency control clockwise slowly. It will be noticed that images will be formed on the face of the scope with the pips displaced downward from the horizontal sweep. As the control is advanced, first, four pips will be formed, then three, then two, and finally one. When one image is formed, it will be found that it will be almost impossible to make that pip appear stationary on the scope. Get it as steady as possible, then slightly turn the sync control clockwise, and it will be found that the image on the scope will

8. Turn the remote-local switch (14) to LOCAL, and the height of the grass and the echoes may be controlled by the receiver sensitivity control (10), located on the front panel of the receiver. Turn the receiver turning control (9) back and forth until the pips come to a maximum, and decrease on each side of the maximum point. By going back and forth over this point several times, it is possible to find accurately the position of the knob which gives maximum echoes on the test scope. It is best to tune on small echoes and get them as big as possible.

Note. For precise tuning, it is absolutely necessary that no one move the antenna while the receiver is being tuned, either in train or elevation. It is also highly desirable that the echo used to tune the set be a steady pip from a land target. This is the only tuning adjustment the operator need know. Further tuning requires the more extensive knowledge of the maintenance man.

CALIBRATION

Range zero set.

1. To show accurate ranges, it is necessary that the range dial be accurately calibrated so that zero range on the range dial corresponds to zero range on the scope. Turn the grass to the height usually used in operation (about half an inch), and turn the image spacer knob (2) completely clockwise.

2. Turn the range dial to the zero set given by the technician. It is a minus value of range, usually about minus 200 yards, at which the range dial is set, (A value of minus 200 yards is the same as a range of 99,800.)

4. Turn the outer knurled nut (2), and move the image across the scope until the left-hand edge of the transmitted pulse coincides with the left-hand edge of the notch. Adjust this nut until the left-hand edge of the notch falls half-way down to the bottom of the notch.

Figure 4 Mk. 3/Mk. 4-5. Transmitter pulse position for correct zero set.

5. Check to see if the range dial is at the zero set. and then carefully tighten the smaller knurled nut with the right hand, while holding the larger nut with the left hand to prevent it from turning.

6. Crank the pulse out of the notch, then crank it back to the position described in step 4 above, and check to see if the zero set has slipped while tightening up the smaller nut. If it has slipped, repeat the above procedure until the correct setting is obtained.

Note: The above procedure should be practiced until an accurate zero set can be made very rapidly. During the first half-hour after the radar has been turned on from completely off, the zero setting should he checked at least as frequently as once every two minutes if accurate ranges are necessary during this time. After this time has elapsed, the zero setting may be checked less frequently. After three hours, the zero setting may be checked about once every half-hour, and always before each firing run in gunnery practice or battle, if practicable.

(See Part 1. General Radar Principles.)

1. Train on another ship-the larger the better, on a course parallel to your ship and not more than 2,000 yards from it. (Between large ships, greater distances may be used.)

2. Start getting ranges on the other ship. It is important that the pointer and trainer remain right on the target during the following procedure.

3. If the other ship is close enough, two pips will be observed on the range scope. The closest pip will be saturated and the second pip will probably be quite small. The second pip will be at approximately twice the range of the first pip. (See fig. 4 Mk. 3/Mk. 4-6.)

Figure 4 Mk. 3/Mk. 4-6. Double range echo.

4. The first pip is placed in the notch, and its range is noted. Let us say its range is 1,700 yards. Then the second small pip is placed in the notch, and its range is noted. Let us suppose its range is 3,200 yards. The difference between these two readings gives the accurate range between the two pips. In this case the range would be 1,500 yards. The range to the double echo should be just twice the range to the first echo, since the pulse has had to travel just twice the distance in forming the double echo that it traveled to the first echo. Therefore, the total distance traveled by the pulse in forming the double echo was 3,000 yards, and the distance to the first echo must be half that distance, or equal to the

5. The first pip is then placed in the notch and the range dial is set to the difference between the ranges of the first and second pips (in this case 1,500 yards), by means of the zero adjustment nuts.

6. After securing the zero adjustment nuts, the transmitted pulse is cranked back to the notch and placed as though making a zero set. The minus zero set is noted when the transmitted pulse is as shown in figure 4 Mk. 3/Mk. 4-5.

This zero set should be written down in a conspicuous place near the range unit, as it is the zero set that should be used. Steps 4, 5 and 6 should be executed as quickly as possible and repeated several times until consistent results are obtained. Occasionally, there will be two pips where the double echo should appear, and the range operator may not know which is the true double echo. One of these pips, however, will be clear and the other foggy. The clear one will be the double echo. The reason for this is, that if you are on the target the pip from the target will be clear and not foggy. A foggy target would indicate another ship, sore debris, or another extraneous target which is off the line of sight. Finding the zero set should be done only after the set has been on at least three hours, and is thoroughly warmed up. This is only one method of obtaining your zero set. Other methods are described in BuOrd Pamphlet No. 657.

*Train and elevation calibration.

1. Alignments of the radar antenna with the optics is an easy matter. The trainer and pointer have merely to look through their telescopes when their pips are matched, to see if their cross-hairs cut the target. During an exercise using full radar control, the control officer can determine if the radar is aligned with the optics, by looking through his telescope when the crew gives the word that they are on the target.

2. Level and cross level should always he cut in when aligning the antenna.

3. To align the antenna in train, two men are placed on top of the director with wrenches to loosen the securing bolts, and move the adjusting screws holding the antenna. The trainer and painter

4. The antenna should never be checked for elevation accuracy at angles less than 15 degrees. If it is found to be off, it is realigned by training optically on a plane flying directly to the ship, and passing over the ship. The maintenance man should adjust the microcoupler on the antenna shaft, while watching the pointer's scope, until the pips on the pointer's scope are equal.

5. For more details see BuOrd Pamphlet No, 657.

OPERATIONAL TECHNIQUE

The range operator.

The range operator is the keyman of the FD team. Upon his shoulders rests the responsibility of supplying pips of the proper size to the trainer and pointer. It is up to him to select the particular target the gunnery officer may designate. He must also be able to tell what type of target a certain pip indicates, if a ship, the approximate size; if a plane, its size; if a number of planes, the approximate number in the flight. He must be able to distinguish the pip presented by a submarine from the water return which tends to confuse it. He must be ever alert to detect even the weakest echoes, and he prepared to get his team on them before they disappear.

The two greatest responsibilities of the range operator are: (1) to keep the pip in the notch, and (2) never to let it saturate (flatten on top due to too much receiver sensitivity). The pip must be kept in the center of the notch so that the pip appears even on the pointer's and trainer's scopes. If the pip saturates on the range scope, it will saturate on the trainer's and pointer's scopes, thus preventing them from knowing which way to train or elevate.

One of the range operator's hands should always he on the range knob. When he wants to change range quickly, he should turn the range wheel with the small crank on it. For fine adjustment of range, such as keeping the pip in the notch, the operator should grasp the wheel with his hand and not use the crank. Usually this will be the right hand, but in some installations it may require the left.

The opposite hand (usually the left), should always be resting on the top of the range scope. The

Figure 4 Mt. 3/Mk. 4-7. Pips on trainer's or pointer's scope.

The trainer and the pointer.

The trainer trains toward the smaller of the two pips. (fig. 4 Mk. 3/Mk. 4-7, train left.)

The pointer elevates if his left pip is lower. (fig. 4 Mk. 3/Mk. 4-7, elevate.)

A rule to follow is the Three L Rule. For the trainer: left, low, left; meaning if his left pip is low, train to the left. For the pointer: left, low, lift; meaning if his left pip is low, lift or elevate the antenna.

Some pointers think of the left pip on their scope as an indication of the position angle of the antenna. If the left pip is low (in relation to the right pip, of Course), the antenna is pointed below the target. If the left pip is high, the antenna is pointed above the target. This is a good way to tell the position angle of the antenna.

Sometimes the trainer will be able to match up two pips, but no pips will show on the pointer's scope. This can be caused by minor lobes again, and the trainer should train back and forth until the pointer and the trainer both can see two pips. The angle between the minor lobes and the main lobe is 15 degrees to 20 degrees.

Below 12 degrees of elevation, the ED cannot be relied upon to give accurate position angles. With surface targets we know what the position angle is, and so are not concerned about the inability of the ED to give an accurate position angle. In train there is not this inaccuracy.

Searching with bearings and ranges given.

The approximate bearing and range will be given to the operator by CIC. The approximate range is placed on the range dial. When the director is trained to the approximate bearing, the lobing motor should be turned on, and a search begun through a small angle (15 degrees) for the target. The elevation angle should be varied from zero to about 10 degrees. It is most important that the image spread knob (2) be turned completely counterclockwise. The range operator must be extremely alert to see any echo that may appear along the length of the sweep. He should never allow his gaze to concentrate on one portion of the sweep for too long a time. Echoes frequently appear as a small, straight line, no higher than the grass, and the operator must be quick to notice them. Turning the range knob back and forth slightly helps somewhat, because echoes which ordinarily would be hard to distinguish from the grass become more readily discernible, appearing as small, bright lines, moving back and forth in the grass. The selector switch should not be on RADAR RANGE when doing this.

As soon as the range operator sees the target he should call out "mark," or "hold train and point," so that the pointer and trainer will stop searching. Then, opening the notch with one hand, and turning the range knob with the other, he should rapidly bring the target into the notch at no time losing sight of the target. If the target is at a great range, it will probably disappear by the time the operator has it

Searching when no bearings or ranges are given by the search-radar.

In searching, when bearing and range are not given by the search radar, practically the same method is used as was described in the preceding section. The only difference is in the range operator's use of the sweep gain control. While searching, when you do not know that there are any targets, the sweep gain control should be turned counterclockwise until the trace occupies only about three inches. Targets can still be seen with ease, and this method possesses the advantage that the operator will be able to keep the whole sweep under his eyes at once. An experienced operator will not have to do this as often as an inexperienced operator, since the experienced man can watch alertly the greater trace as easily as the inexperienced man can watch the shorter sweep.

It seems to be the current practice, to keep the lobing motor turned off at all times, except when actually tracking a target. The only valid reason for this is that it saves the lobing motor from excessive wear. This admittedly is important since the lobing motor and cam assemblies are one of the weakest units of the Mark 3 and Mark 4 radars. They are located in a place where it is difficult to work and repairing them properly is a tedious job.

There are many in the held, however, who feel, that the benefits to be derived from operation of the lobing motor for searching outweigh the disadvantages. The greatest benefit of using lobing while searching is that it causes the beam width to increase from 9 degrees, the normal width of the beam, to 15 degrees, the width of the radiation pattern between half-power points with the lobing on. This increased coverage accompanied by no loss in power, since actually

Another reason for keeping the lobing motor on while searching, is that, once a target is picked up, and the trainer and pointer get on it by using optics, the C and I operator will have no need to turn the lobing motor on. He probably could read ranges under this condition, but let us suppose the target was suddenly obscured from view for some reason, as the laying of a smoke screen, or the sudden appearance of a rain squall. The trainer and pointer would immediately turn to their radar to track the target, and it might take some time to determine that their lobing motor was not on, and another period of time to line up their scopes. In the excitement of battle, working under nervous tension, such a delay might easily be prolonged. Any delay, however slight, at such a time, might very well change the outcome of a battle. So if such a delay can be eliminated, even at the expense of giving the maintenance men additional work, it should be done, and the lobing motor should he left on.

When the lobing motor is turned off, the beam, which was being swung in four distinct positions, gradually comes to a stop. It might be pointed up into the air or down into the sea. It might be pointed to the right or left. There is absolutely no accurate method of telling just where the beam is pointing. In any case, it never comes to rest pointing along the line of sight. Thus you might be searching for a ship with the beam pointing up into the air. However, if you turn your lobing motor on when searching your beam will be swung in all four positions, and you can always be sure you will not miss your target because you know your beam is pointed in the right direction.

Tracking.

Gradually the pip will become strong enough that it may he continuously tracked. When this occurs, the computor may be switched in, if full radar control is desired. As soon as the target is close enough to appear in the pointers and trainer's telescopes, the optical rangefinder should notify the control officer, and the trainer and pointer should switch over to their optics. Radar ranges should be used whenever possible, since they are more accurate than optical ranges. Furthermore, radar will give the range to the target continuously, whereas most stereo-rangefinders have to put their reticules back and forth over

After the range operator has picked up the target and told the pointer and trainer to "hold train and point," he cranks the pip into the notch as described above. When it is in the notch, he says loudly, "on target." This indicates to the trainer and pointer that he has a pip in the notch and they accordingly look closely for it. When they have their pips matched up, they each say "mark." They continue saying "mark" whenever their pips are matched, and the range operator continues to say "on target," whenever he has the pip in the notch and the pointer and trainer are still using their radar.

Another good method is for the range operator to say "on range"; the trainer, "on train"; and the pointer, "on point."

The control officer will instruct the range operator as to the procedure and doctrine of pushing the range button. This range button is located in the center of the range knob and, when pushed, signals plot that the range is on at that instant. It also activates the range rate mechanism.

Spotting.

It is possible to see the shells leave the guns of your ship and follow them for quite a distance on the scope. Sometimes they look like "mice running under a carpet." Usually, they appear as distinct pips and move across the scope. You can also see shells from the enemy coming toward you on the screen. That should not prove too disconcerting, since they could miss your ship by quite a distance and still appear to be coming toward it,

The range operator has the additional function of spotting misses. This is done by estimating the distance from the target's pip to the pip produced by the miss. The notch should be completely expanded. The width of the notch and the width of the expanded portion of the sweep should be determined for the operator's set. This can be accomplished by cranking an echo, or the leading edge of the transmitted pulse across the notch or sweep, and noting how much range was covered on the range dial. The notch is generally about 600 yards wide, and the expanded portion of the sweep about 6,000 yards. If the set is in perfect operating condition, the notch should remain in the center of the C and I scope. You can estimate the spot by mentally comparing the distance from the target to the splash with the

Determining composition.

Skill in identifying targets by means of their pips is largely developed by experience. Aircraft pips flutter up and down vigorously. Their bearing, range, and elevation change rapidly. Clouds and atmospheric conditions which sometimes give echoes similar to planes are easily distinguished by means of their slow change in bearing, range, and elevation. Sea-return, which also looks like planes, usually appears within 2,000 yards, and it is impossible to obtain a bearing on it. Two planes flying together produce a beating effect, and their pip will bounce up and down with some regularity. A group of planes will produce a large echo which is never clear inside. They can be picked up by a good operator at 90,000 yards if they are high enough, and the set is operating properly.

The range to surface targets is limited by the horizon. Ships produce pips which will fluctuate up and down rather slowly; the larger the ship, the slower the fluctuation of the pip. They change range and bearing (but not elevation) slowly. Land targets are steady and strong. Sometimes land echoes will fluctuate like planes or ships. Good judgment together with experience will enable you to identify such pips as echoes from land. Satisfactory results cannot always be obtained when tracking a sleeve, for the sleeves in current use give echoes too weak to be used properly.

If the radar team must be coached on to the target by means of optics, they are knowingly passing up one of the greatest advantages we possess over the enemy. Radar should always pick up the target when it is far beyond optical ranges. Remember, that your skill as an operator will increase with practice. When you are able to distinguish an SBD from a TBF by the difference in their pips, you have really accomplished something.

Anti-jamming technique.

Oilier radars may produce interference on the range scope. This, as well as electrical faults in the set itself, can produce effects which might be called jamming by the inexperienced operator. If the interference is caused by the transmitted pulse from another radar set, an occasional pip will move across the screen in either direction. Effects which occur on all bearings or on the same relative bearing should also be

If the range scope seems to be jammed, report the fact immediately to the control officer, and also to the maintenance man. Continue to try to work through the jamming. Turning your lobing off may help. Sometimes the narrower antenna beam resulting when lobing is off will enable the operator to direct the beam on the target alone, and not on the target plus the jammer, as might well happen with lobing on, and double the area being covered. Thus the operator might be able to range on the target, but he would have to turn the lobing on again to get a bearing. Vary your receiver sensitivity control (3) carefully to determine the optimum setting. Return the receiver sensitivity control to its normal setting when the jamming ceases, or when operating on unjammed bearings. This is important, because targets may sometimes be visible at low sensitivity control settings in the presence of jamming, but completely absent at the same sensitivity control setting when the jamming ceases.

It is possible to train on the jamming station by simply matching the height of the jamming in the trainers pips. Remember, that the jamming will probably be much stronger than most echoes, and will tend to produce saturation signals. Therefore, when matching pips in jamming be sure that the gain control is turned down sufficiently, otherwise it will be difficult to pip match. Two ships can thus get a fix on the jammer. The pointer should also match the jamming on his scope. Remember though, minor lobes are much more important when being affected by a jamming signal than they normally are. So be very careful when using this method that you do not get on a minor lobe when matching up the height of the jamming on the two scopes.

Rotate the antenna to determine whether the jammer and the target are on the same bearing. If they are not on the same bearing, a pointing and training error of several degrees or more is to be expected, even if it is apparently possible to match pips. Report this to CIC. When the target and jammer are less than 5 degrees apart in bearing it will be difficult to determine whether the jammer is on or off the target bearing. The accuracy of range information is not seriously affected by jamming on any bearing, but it will, of course, be more difficult to obtain. It will be found that the pip matching scopes are more difficult to interpret than the range scope when jamming is encountered.

The maintenance man can change the frequency of

As pointed out previously, it is of the greatest importance to keep trying to work through the jamming. The jammer will have to stop operating occasionally to check your frequency. in order to see if it has been changed. The second he stops jamming, obtain ranges and bearings (sometimes position angles), on the target. You must keep alert in order to get on the target almost instantly.

Some sets have an anti-jamming modification installed in the C and I unit. Turning this device on will sometimes improve the C and I scope. Always remember to cut all anti-jamming devices out of the circuit when no jamming is present.

Never give up hope. Look for small discontinuities in the jamming, they might well be echoes. The British have shown that good jamming is extremely difficult to carry out successfully. So keep trying to work through the jamming, be patient, and above all do not get excited. A cool head is the best anti-jamming device ever discovered.

RELIABLE RANGES OF MARK 4 RADAR

Maximum reliable ranges.

The tables on the opposite page show the maximum reliable ranges of the Mark 3 and Mark 4 Radar. The figures given are the averages of many ships reporting. These data are taken from BuShips' publications.

A good crew with well-maintained sets should he aide to get considerably better results than these.

Minimum ranges.

On ship targets the minimum range is 800-1,000 yards. The minimum range on aircraft is 1,100-1,700 yards.

Accuracy characteristics.

The following table is taken from BuOrd Pamphlet No. 657, and shows the accuracy-resolution characteristics of the Mark 3 and Mark 4 Radar, using three different antennas.

Resolution.

The range resolution of the Mark 3 and the Mark 4 is 400 yards. The bearing resolution of the Mark 3 (3' x 12' antenna) is 5 degrees. The bearing resolution of the Mark 4 is 10 degrees.

These are important figures, and they should be kept in mind at all times. If a target is greater than 400 yards offshore, a Mark 3 or Mark 4 will distinguish the target from the land as long as the line of sight to the target is perpendicular to the shore line. In this ease, only the range resolution of the set is being used. If, however, the line of sight is

The same dependency on accurate knowledge of the range and bearing resolution also conies into effect when there are a number of ships steaming in column making a target angle of 90 degrees or 270 degrees. If the ships are close together they will appear as one pip on the range scope. If they made a target angle of 0 degrees or 180 degrees they would have to be separated by 400 yards to be seen as distinct pips.

Many similar applications of these principles will he obvious to the thoughtful operator. For example, suppose that a ship is stationed off the mouth of a harbor or large river waiting for the enemy to come out. Assume the target to be midway in the mouth of the passage. So long as the shores did not intercept the two lobes (as they would if the channel were narrow or the target close to one side), land at the same range as the target would appear on the range scope, and it would be difficult to range on the target itself. Let us also suppose that two planes are coming toward your ship, both at the same range and close together. If they are not too far apart (subtending an angle of less than 10 degrees) the radar, unable to distinguish each individual plane, would train at a point midway between them. The same would be true of two ships.

Figure 4 Mk. 3/Mk. 4-8.

When the scope will not light up, or there is no transmitted pulse, it is obvious at once that something is wrong with the set. However, there are many minor malfunctions which only the experienced operator will notice. For example, when the image spread knob on the range scope is varied, that is, if tile position of the notch (not the width) moves across the face of the scope, and does not remain in the exact center of the sweep, the set is not functioning properly. (In this ease, the 29.5 KC and the 1.64 KC gears in the range unit may need realigning.)

Sometimes a false echo is seen at about 50,000 Yards on the range-scope. This can readily be detected as a "ghost," since it is present for all angles of train. (In this case, the fault may be caused by parasitic oscillations in the 807 tubes in the modulation generator. It can be removed by changing tubes or by soldering a small piece of wire to the cathode connection of one of the tube's sockets.) Double humps in the pips can be caused by faulty receiver tuning. Often the pips will saturate too soon on the trainers and pointer's scopes. In other words, the pip will only seem F-3 on the range scope, yet will be saturated on the other scopes. (This can be remedied by changing R88 in the C and I scope from 2K ohm to 1,200 ohms.)

All these are minor faults, yet for peak operating efficiency they must be eliminated. An operator should consider it an important part of his job to see to it that the set is kept in the best condition at all times.

SA RADAR

Like all other radars, the SA is a complex instrument, requiring careful and precise adjustment and operation. Many of the adjustments should be made by the operator, and the controls are conveniently placed so that this may be done.

The controls with which the operator must concern himself may be divided into five main classifications: power controls and indicators, selector switches, operating controls and indicators, adjustments, and alarms. The majority of these controls arc found on the receiver-indicator panels, which are located at the operating position. A few of these controls are mounted on the transmitter unit which is usually installed elsewhere in the ship. One control (on-off switch) is mounted on the train control amplifier cabinet.

The various controls and associated meters and dial lights are listed and explained below. Their arrangement is shown in the accompanying drawings.

Power controls.

P-1. Main power switch (labeled main power emergency): controls all power to the set except that to the heaters. Power is applied to the set when this switch is in the UP position.

P-2. Line voltage meter.

P-3. Line voltage variac: controls the voltage applied to the set. It should be adjusted so that the line voltage meter (P-2) reads 115 volts continually.

P-4. Transmitter power switch (labeled plate voltage): applies the high-voltage to the plate voltage variac when in the UP position.

P-5. Plate current meter: indicates the DC current flowing through the transmitter tubes.

P-6. Plate voltage variac: controls the voltage applied to the transmitter tubes. (The numbers around this knob indicate only relative voltages, and not actual amounts.)

P-7. Fuses (labeled "5 amp. fuses") : these fuses are in the power line to the lobing and slewing motors. If either or both should blow, the antenna must be rotated by manual control or by the emergency train motor (control S-2). Lobe switching is impossible when fuses are open.

P-8. Fuse (beside dimmer control) : protects the

P-9. Emergency off (on transmitter) : this switch opens the high voltage circuits in the transmitter.

P-10. Plate current meter (on transmitter): indicates the same thing as P-5 on control-indicator panel.

P-11 Fil. primary voltage variac (on transmitter) an adjustment of the filament voltage applied to the transmitter tubes.

Figure 4 SA-1. Transmitter unit.

P-13. Hours operation meter: records the total time the filament voltage has been applied to the transmitter tubes.

Selection switches.

S-1. Antenna train-relative, true: when in relative position, the antenna will stay on the same relative bearing when the ship changes heading. When in true position, the antenna stays on the same true bearing as the ship changes course.

S-2. Emergency train-CCW, auto. CW: the setting of this switch determines what unit will govern rotation of the antenna. When in auto position, the antenna may be rotated by hand, or controlled by the Mewing motor (control S-3). In either case, power passes through the train control amplifier (TCA). When the switch is in the CCW or CW position, the antenna is turned either counterclockwise or clockwise (respectively) by a motor which does not

S-3. Slewing motor-low, off, high: when switch S-2 is in auto position, this slewing motor switch permits automatic rotation of the antenna at either of two speeds (1 rpm or 4 rpm), or manual rotation of the antenna.

S-4. Range sel (range selector): setting of this switch determines the range scale being used: 30,000 yard scale when in position A, 75 miles when in position B, and 375 miles in position C.

S-5. Cal-fid IFF: the setting of this switch selects the picture seen on the screen. When in cal position (extreme CCW), range markers appear. When in the No. 2 position, the usual "A" scope picture appears, but maximum strength of the pips is limited so that the PPI scope (if any) will not be damaged by too much echo intensity. Position No. 3 is the same as position No. 2, except that maximum pip height is greater. Position No. 4 is used only when challenging a target for IFF response. It operates the interrogator (at present, the BL), and removes the range step.

S-6. Cal synch (calibrate, synchronizing switch): this switch, with switch S-5 controls the picture on

S-7. L.R. motor-on, off, on: this switch controls the lobing motor. The lobing motor is turned on by switching to either the left (CCW) or right (CW) position. The lobing motor (left-right motor) is off when the switch is in the OFF (center) position.

S-8. L.R. off: this switch makes normal search possible even while the lobing motor is on. When lobe switching (L.R. motor is on), two traces from each target normally appear on the screen. However, when searching, too pips would be confusing, so this switch is used to permit blanking of the right-hand trace when thrown to position 1. When in position 2, both pips appear.

Operating controls and indicators.

Op-1. Range oscilloscope (the scope) : the cathode-ray tube used to indicate presence of the echoes and to permit ranging on these echoes.

Op-2. Yards range counter: indicates the range in yards, corresponding to the step position on the scope when control S-4 (range selector switch) is in position "A" (or, in other words, when set for a 30,000-yard nominal range).

Op-3. "B" miles range counter: dials indicate the range, in nautical miles, corresponding to the step position on the scope, when control S-4 is in position B (for a 75-mile nominal range).

Op-4. "C" miles range counter: indicates the range corresponding to step position on the scope when control S-4 is in position C (or for a 375-mile nominal range).

Op-5. Range step control: this knob controls the position of the step on the range scope, and the corresponding reading of the numbers on the range counters.

Op-6. Bearing indicator: indicates the direction of antenna train, with the outer dial indicating the relative hearing, and the inner dial the true bearing (if control S-1 is in TRUE position and gyro compass is operating properly). Two diamonds, or bugs rotate with the antenna; the orange bug should he read when adjusting for the maximum pip, and the

Op-7. Manual antenna-train knob: this knob makes it possible to rotate the antenna manually to any bearing desired, so long as control S-2 is in the AUTO position. When control S-3 is in either the LOW or HIGH position, the antenna rotation may he stopped or reversed by operating this handle.

Adjustments.

Ad-1. Focus: controls the sharpness of the picture on the screen of the range scope (Op-1 ).

Ad-2. Astig (Astigmatism control): no single setting of the focus control (Ad-1) can bring all parts of the sweep into correct focus. This control permits the operator to bring any desired part of the sweep into a sharper focus. The astigmatism control may he considered as a fine adjustment of the focusing.

Ad-3. Intensity: controls the brilliance (or intensity) of the trace on the screen of the range scope.

Ad-4. Horiz (Horizontal centering control): the complete trace on the range scope (Op-1 ) may be moved horizontally by adjustment of this control.

Ad-5. Vertical (Vertical centering control): the complete picture on the range scope may be raised or lowered as the operator desires, by means of this control.

Ad-6. Oscillator adjustment oscilloscope (the 2inch oscilloscope): the scope used to indicate when the calibrating oscillator is adjusted to the right frequency (so that the range marks will have the proper time interval). Control S-6 must be in position 3 for any picture to appear on this scope.

Ad-7. Oscillator ad just meet oscilloscope focus: permits focusing the picture on the osc. adj. screen.

Ad-8. Cal. osc.: controls the time interval between the range marks (by controlling the frequency of the calibrating oscillator). This, of course, changes the picture on the osc. adj. (Ad-6).

Ad-9. Cal max.: controls the speed of the sweep (travel of the spot of light across the screen) on the range scope. Changing this speed gives the appearance of crowding the range marks closer together, or spreading them farther apart.

Ad-10. Cal min.: permits moving the range step along the time base without moving the range counters, so that the range counters will indicate the correct range.

Ad-11. Dimmer: adjusts the brightness of the dial lights.

Ad-13. Second R.F.: another adjustment of the receiver tuning.

Ad-14. Osc.: tuning control of the "local oscillator." Another receiver tuning control.

Ad-15. Ant.: adjustment to tune the input circuit to the receiver.

Ad-16. Calibration chart: lists settings which are approximately correct for controls Ad-12, Ad-13, Ad-14, Ad-15. These four tuning controls should he adjusted for the greatest echo strength. (There are four sets of settings-only one will be correct for a particular radar set. The technician decides which set of readings to use.)

Ad-17. IFF gain: the "volume control" of the IFF receiver, since it adjusts the size of the IFF pips on the range scope screen as the operator desires.

Ad-18. L.R. amp: controls separation of the two blips from a target when using lobe-switching. To he effective, control S-7 should he ON, and L-R off in the ON position.

Ad-19. Duplexer adjustment (on transmitter) tunes the duplexer (a part of the antenna connections).

Alarms.

Al-1. Bearing mark: a push-button which rings a buzzer on the bridge when the operator wishes to call attention to the remote bearing repeater.

Al-2. Range mark: sounds alarm at the remote range repeater to call attention to the range indicated.

TURNING ON AND OFF

Turning on.

1. See that these controls are in the proper position.

2. Snap on the main power-emergency switch. The dial light on the line voltage meter will come on. Adjust line voltage control so that this meter reads 115 volts, The blower motor in the transmitter will start, and the red lights on the TCA and the transmitter will go on.

4. Now snap transmitter power switch ON (up). The plate current meter should light up.

5. While watching the plate current meter, turn the plate voltage knob clockwise until the meter shows a sharp dip. Continue raising the plate voltage until the 5-7 milliamperes is read on this meter, or until the present stop is reached. If the overload relay trips while doing this, it may he necessary to lower the plate voltage, reset the relay in the transmitter (click emergency switch on the transmitter off, then on again), and continue operation, using a lower plate current.

Turning off.

1. Turn plate voltage variac fully counterclockwise.

2. Snap transmitter power switch to OFF position.

3. Turn off main power switch.

CALIBRATION

1. If the cal-synch switch is in position 2 and cal-fid-IFF is in position 2, 3 or 4, the transmitter pulse will be visible on the scope when gain is increased.

2. Snap cal-fid-IFF switch to cal (No. 1) position and cal-synch switch to position 3. The trace will disappear from the range scope. Adjust focus (No. Ad-7) control until some indication appears on the 2-inch scope.

3. Now adjust cal-osc control until a stationary pattern appears on the 2-inch scope. Either a figure eight pattern or a horizontal V is satisfactory.

4. Then turn focus (No. Ad-7) control so that this picture disappears and snap cal-synch to position 2. Range marks should again he visible on the range scope. Snap range selector switch to the A position (30,000 yards).

5. Set the range counters to read precisely 6,000

Figure 4 SA-3. Pattern for calibrating minimum range on 15,000-yard scale.

6. Adjust cal-max until the counter reads 26,000 yards when the step is lined up with the beginning of the seventh range mark. (sec fig. 4 SA-4.)

7. Repeat steps 5 and 6 until no further adjustment is necessary to make the step read correctly at either end, then snap cal-fid-IFF switch to position No. 2.

Figure 4 SA-4. Pattern far calibrating maximum range an 15,000-yard scale.

OPERATIONAL TECHNIQUE

Tuning the receiver.

Increase the receiver gain until some grass appears. If any targets are present, adjust OSC., 2nd R.F., and 1st R.F. controls until the pip appears largest. Unless some target is present to tune on, this step should not he attempted. Sea-return is a "target," if visible, and you can tune on it-using the short range scale. If no targets are available, and set is known to be out of tune, set controls as listed on the calibration chart (Ad-16).

Move the step until the range counters read 40 miles. If the step is not accurately lined up with the 40-mile mark on the transparent-tape scale, adjust horizontal centering control until it is. (Operate

Now begin to search by starting the antenna rotating either automatically or manually.

Miscellaneous adjustments.

If lobe switching is to be used, turn plate voltage control completely down (counterclockwise), snap L.R. motor on (either to right or left), and wait one complete minute before again raising the plate voltage, except in emergencies; the voltage may be raised after about 30 seconds. Snap L.R.-off switch to ON position (No. 1) and adjust L.R. amp. control until the traces are separated suitably. While matching pips, read the white bug.

If IFF equipment is used with this set, turn the IFF equipment on, snap cal-fid-IFF switch to position 4, and adjust IFF gain until a reasonable amount of grass appears below the time base, then set cal-fid-1FF back to either position 2 or 3 until ready to challenge a target. Snap cal-fid-IFF switch to position A to challenge a target.

Long-range search.

The SA radar was designed primarily for long range air search-an early warning of approaching aircraft. Its effectiveness depends not only on the materiel condition of the equipment, but also on the efficiency of the operator. The following search procedure permits the set to be used efficiently and effectively.

Search first on the 75-mile scale, using low speed automatic antenna rotation. Keep the gain fairly high (at least one-sixteenth of an inch of grass), and watch for very weak pips. The lobing motor (L.R. motor) should be kept off. Continue searching on this scale and in this manner for about four minutes, then make one or two complete rotations of the antenna using the manual antenna control, studying the trace very carefully.

Next switch to the A-scale (30,000 yards), and search for two complete antenna rotations, looking especially for small pips which may not have been on the B-scale. Use manual rotation of the antenna for the second turn of the antenna. Readjust the gain and astigmatism controls slightly, if a clearer, sharper trace is desired. Low flying planes may be detected first on this scale.

Again search on the B-scale for about five minutes, as outlined above.

Then use the C-scale (375 miles) for two rotations of the antenna, using manual control. Pay particular

The procedure described above must be used when operating independently. A somewhat different procedure is required when serving as radar guard ship. In this case, the O.T.C, will state whether search should be made using only the 75-mile scale or only the 30,000-yard scale. The antenna should not be stopped on a target except for a few seconds (while challenging for IFF, etc.), without specific instructions from the O.T.C.

Searching over land.

If search must he made over land, target pips will be mixed with the land pips. However, planes will give echoes which bob up and down more rapidly and irregularly than the land pips. Also, the plane pips will move with respect to the land pips. When faced with the problem of searching over land, the antenna may be stopped for a few seconds to determine whether the pip is actually behaving as a plane echo or as a land echo. Bearings cannot be obtained very accurately, but the bearing of maximum swing of the pip should be reported. Land masses may cause the pip to be higher on a bearing a few degrees to one side of the actual target bearing, and so maximum pip height may not give the correct indication-it is the maximum bounce that counts. The approximate bearings secured are well worth the effort expended to get them.

The operator must remember to keep searching. He should not find one target and "camp on it" from then on.

Reading bearings on the fly.

With practice, almost any operator can read the bearing of an object with considerable accuracy even though he does not stop the antenna. This speeds up tracking and makes the SA radar much more effective.

Any experienced operator can tell when the pip on the scope first begins to drop off as the antenna scans past the bearing of the target. If he then glanced at the bearing indicator and read the bearing indicated, he would be reading a bearing somewhat large (for CW rotation of the antenna), because of the delay before reading the bearing. The size of the error involved would depend upon the time required by that particular operator to realize that the pip height had begun to drop off and then to look at

Assume that the operator has the antenna set for low speed automatic rotation, clockwise, and knows that the antenna rotates nine degrees after the pip first begins to drop off in height, and before he can read the bug. He watches the pip increase in size, and then begin to drop off, he immediately reads the bug, silently. If he read "one-nine-seven," he would subtract nine degrees (his "personal error") and call off "one-eight-eight."

When the pip first appears, the range can be read immediately and remembered. As soon as the bearing has been reported, the operator can call off the range without hesitation and with no need of again looking at that pip until the antenna gain approaches the bearing of that target. With practice, this reporting procedure becomes almost automatic.

Operators must make every effort to learn this method of reading bearings. They must practice until the delay in reading is unchanged each time they report. (In other words they must not slow down or speed up glancing from the scope to the bug.) To find their own lag, they should first watch the pip grow in height, read the bug, and then use lobe switching to find the accuracy bearing. Comparing these two readings will indicate the amount of correction to be applied each time. This must be repeated over and over again, until the operator gets the same correction (within a degree or so) each time.

This is not as difficult as it sounds. It does take practice, but results are well worth the effort involved.

Tracking.

Targets probably will be contacted first on the 75mile range scale; hence, this is the scale most often used for tracking. The addition of a transparent tape range scale to the scope, makes accurate tracking of several targets relatively quick and simple. Tracking while using this 75-mile scale will he discussed first.

When a pip appears, stop the antenna approximately on the target, but do not waste time getting an accurate bearing. Read the bearing indicated by the orange bug, and note the range indicated on the

When the contact is identified as friendly or bogey, start the antenna rotation at slow speed, automatic, and continue searching for other targets. When the pip from the first target reappears, note the range immediately from the scale on the scope, and read the bearing "on the fly." This report should be made every time the pip appears, reporting the bearing first and then the range.

Keep in mind the number of targets present, and if one fails to appear when the antenna scans past its previous bearing, report it as being "in a fade."

Generally speaking, there is no reason for changing from the 75-mile scale while tracking. Even after a plane, or group of planes, has closed well within 30,000 yards, the 75-mile scale is still sufficiently accurate and much more easily read than the 30,000-yard scale,

If a target is first discovered at a range greater than 75 miles, tracking must be conducted using the 375-mile scale. This requires stopping the antenna on the bearing of the target and using the range step, then starting the antenna once more. When the target closes to within 75 miles, use the 75-mile scale, as explained above.

If a plane is discovered while searching on the 30,000-yard scale, give the initial contact report and continue searching. If the pip can be seen clearly on the 75-mile scale, that scale should be used in tracking. Search must be continued while tracking air targets.

Fire-control liaison.

Use of the SA radar for anti-aircraft fire-control is limited to warning of the approach and tracking the targets (getting course and speed). However, this radar is useful in surface fire-control work, for it gives ranges and bearings which may be used in an emergency for this task. In any event, it gives information sufficiently accurate for star shell illumination of surface vessels.

When the SA radar is used for this work, lobe switching should be employed and ranges read from the 30,000-yard range counter.

The actual tracking procedure would be for the plotter to call "stand by" every 25 and 55 seconds after the minute, followed by "mark!" on the minute and half-minute. The operator should read true bearings as indicated on the inner scale by the white bug during the tracking. When directed, to do so by the CIC evaluator, he should report ranges, relative bearings, and read the enter dial, to the gunnery officer. He should read these ranges and bearings continuously.

Jamming and deception.

There is no doubt that the enemy considers our radar an extremely dangerous weapon, and consequently it is only reasonable to expect him to try every means possible to make it less effective. He may use two tactics to do this: jamming and or deception. Every operator should learn how to recognize these countermeasures, and expect them when in combat zones.

When the enemy broadcasts radio signals intending that our radar receive them, and they show a confusing pattern on the screen, it is called jamming. Use of dummy targets (tinfoil, kites, balloons, etc.) is called deception. Of course, more precise definitions are sometimes given, but these are satisfactory for this discussion.

The SA radar can be jammed, and it will show echoes from the tinfoil the enemy sometimes throws out to confuse the operator. The operator should not become alarmed when either of these things happen.

If you were suddenly confronted with jamming, without previous experience, it would appear impossible to work through. However, it is not really that serious if the following procedure is carried out:

The first reason for obtaining a bearing on the jamming is to determine whether or not it could be accidental interference. Jamming will not only be

Try moving the gain control up and down. This is probably one of the most important countermeasures that can be taken, and the one most commonly overlooked because of its simplicity.

In most cases, except when effective noise modulated jamming is being encountered, there is a setting of the gain control with which it is possible to range on a target in the presence of heavy jamming. If there are several echoes on the same bearing, the best setting for each echo is different. Of course it is more difficult to obtain these ranges because of the distortion of the echo produced by jamming, but it is, after all, possible to obtain the desired information. However, the extra effort is worth while because the enemy would not be jamming unless he were trying to conceal something important.

The two general methods of using the gain control, both of which should be tried, are as follows:

Be sure to return the gain control to its normal setting when no jamming is present, or when the antenna is turned to an unjammed bearing.

Try changing receiver local oscillator tuning. When you change the oscillator tuning, you lose some of the height of the desired echo. However, if the jammer is not exactly on your radar frequency, there is a chance that you will detune the jamming signal more than the echo signal. Considerable improvement can sometimes be obtained this way. Try "swinging" the oscillator tuning dial in both directions, to see which direction makes the greatest improvement. Note the correct setting of the oscillator dial so that it can be returned to its normal position when no jam is present, or if detuning does not help, otherwise the radar will not give optimum performance.

Even if the jamming is extremely effective keep operating. Don't turn your radar off. Turning your radar off informs the enemy that his jamming is effective, and certainly makes the radar completely worthless. The effectiveness of the jamming may

Report nature and bearing of jamming to CIC. Recognizing the type may be difficult because nonsynchronous patterns sometimes appear blurred beyond recognition. Inasmuch as knowledge of jamming types* may possibly help identify the jammer in some cases, this information should he reported.

If the equipment is provided with an anti-jamming receiver, the jamming may he reduced sufficiently for reading targets without any detuning of the receiver. Detuning should be a last resort, and then should he done very carefully and cautiously, otherwise all targets may be lost and the equipment made completely ineffective. No set procedure is offered for setting the controls of the AJ receiver, except that they should be varied for maximum readability through jamming, the gain control coming first, and then the AVC control followed by Rej 1 and Rej 2.

Above all, never off the radar.

When jamming/and or deception is encountered, full 360 degrees search must be continued. However, the antenna should be stopped for short intervals from time to time in order to try reading through the jamming (using the "A" scope). You also must be prepared for any diversionary tactics, for the enemy may or may not use jamming and or deception to divert your attention from the bearing of the main attacking forces. This problem is simplified somewhat when similar but separate radars are used for reading through jamming and for searching.

PERFORMANCE

Maximum reliable range.

Antenna 89 feet

Target

Range accuracy.

When using the step and the 30,000-yard scale, the accuracy is about +/- 100 yards. When using the 75-mile scale and reading ranges from the transparent tape, the accuracy is about +/- 1.0 mile.

Bearing accuracy.

With lobing +/- 1 degrees
Without lobing +/- 3 degrees - 5 degrees

TROUBLES

Probably the most frequent failure of SA equipment, is the failure of the oscillator tubes in the transmitter. The operator can easily recognize this because the plate current meter does not show a dip when the high voltage control is turned up. One, or both tubes must be replaced when this happens. Usually, failure will be gradual. The operator should notice when the plate current rises more rapidly than it does normally as the high voltage is increased, since this indicates that the tubes are going bad. The small white spot on the high voltage knob (No. P-6), indicates how high the high voltage has been raised.

When signals appear very weak, or when no targets appear, even though land or other objects are in the vicinity, a receiver tube may not be working. The transmitter pulse may appear at its "normal" strength, even though one of these tubes is not functioning, but echoes will not appear.

If the antenna fails to rotate when either the manual control knob is turned or when the automatic control is on, the train control amplifier probably is not operating properly.

Sometimes one or both of the 5 amp. fuses (No. P-7) will open. When this happens, no power can be applied to the lobing motor (L-R motor), or to the automatic antenna train motor. The ten amp. fuse (No. P-8), near the dimmer control carries power to the indicator unit. If the trace should suddenly disappear from the indicator screen, and the dial lights go out, this fuse has probably blown.

If the ship's gyro compass should fail, immediately throw antenna train-relative, true switch to relative position.

If the bug fails to move when either the manual or automatic antenna rotation controls are used, snap emergency train switch to either CCW or CW position.

SL RADAR

SL RADAR

CONTROLS

Power controls.

P-1. Power: controls all power to the set (except heater power) . Power is off when this switch is snapped to the left (or to the right on some models).

P-2. Load voltage meter: indicates the voltage applied to the set.

P-3. Line voltage adjustment; an adjustment of the load voltage (the transtat). (Adjustment governs reading of load voltage meter.)

P-4. High voltage: this switch turns the high voltage on or off: ON to the right. OFF to the left.

P-5. Mag. or conv. current: current: this meter indicates either the magnetron current or the converter current, depending on position of the ammeter-mag. conv. switch.

P-6. High voltage adjustment: this controls the amount of voltage applied to the transmitter. (It is called the variac. Setting of this control governs reading of the ammeter when in mag. position.)

P-7. Drive motor: this switch controls power to the antenna drive motor and to the indicator motor rotating the sweep (in synchronism with the antenna)

Selector switches.

S-1. Range: a three-position switch, permitting use of one of the three range scales provided: 5 miles, 25 miles, or 60 miles.

S-2. Ammeter-mag. conv.: a switch which permits use of the same meter to indicate either magnetron current or converter current.

S-3. Warning: a switch used to operate a warning bell or buzzer at some remote location, to attract attention to the remote PPI scope.

S-4. IFF-off, on: this switch applies power to the interrogator (if one is attached).

S-5. Compass-on, off: (Under indicator panel -below cony, current meter) in the ON position, this switch permits connecting the gyro compass to the radar so that true bearings will be indicated, regardless of the changes in ship's heading. If relative bearings are desired (or necessary, due to failure of the gyro compass), this switch can be turned to the OFF position, disconnecting the gyro compass.

A-2. Brightness: a screwdriver adjustment of the over-all brilliance of the trace on the screen.

A-3. Focus: a screwdriver adjustment to bring the sweep into a sharp, clear, and even line.

A-4. Horizontal centering: a screwdriver adjustment shifting the complete picture on the scope to the right or left.

A-5. Vertical centering: a screwdriver adjustment shifting the complete picture on the scope up or down.

Figure 4 SL-2. Indicator modulator assembly.

A-6. Receiver gain: this is the volume control of the receiver, and as such, it controls the brightness of the echoes on the scope, and in addition, the brightness of the time base.

A-7. Receiver tune: this permits accurate tuning of the receiver to the transmitter frequency so that echoes may be received.

A-8. Scale light: permits the adjustment of the brightness of the dial lights on the meters and behind the amber shield over the scope.

A-9. Azimuth mark, increase: controls the brightness

A-10. Range mark: controls the brightness of the range mark which should appear at the outer edge of the scope.

A-11. Retard: indicator, antenna: these push button controls permit setting the azimuth mark to any desired direction on the screen (to 000 degrees when relative bearings are to be read, and to the ships heading when reading true bearing).

The indicator button stops the indicator while the antenna continues rotating, and consequently makes the azimuth mark move counterclockwise.

The antenna button retards the antenna without stopping the indicator, and this makes the azimuth mark move clockwise.

A-12. IFF gain: controls the strength of IFF response applied to the SL screen.

TURNING ON AND OFF

Turning on.

Check controls for normal positions:

1. Rec. gain-CCW.
2. Azimuth mark-CCW.
3. Drive motor-off.
4. High voltage switch-off.
5. High voltage adjustment-full CCW.

Power adjustments:

1. Turn power switch ON. The dial lights should come on and a motor should begin whirring inside the modulator unit. The scale light control should be adjusted to suit the operator.

2. Adjust the line voltage adjustment until load voltage meter reads 115 volts.

3. Snap the high voltage switch ON and wait for a loud whistling tone (the 800-cycle note). A time delay relay, requiring about one minute to operate, must close before the 800-cycle note will start. As soon as the whistling starts, check the ammeter reading with the ammeter switch in mag. position. if reading is less than 10 milliamperes, turn off the set and call the technician; if above 10 milliamperes, readjust line voltage control until load voltage meter reads 115 volts. Adjust high voltage control until the magnetron current is 15 to 19 milliamperes.

4. Turn drive motor on and listen for grinding of gears.

1. Turn rec. gain fully CCW.
2. Turn azimuth mark fully CW.
3. Turn high voltage adjustment CCW.
4. Turn off high voltage switch.
5, Turn off drive motor.
6. Turn power switch off.

CALIBRATION

Calibration should he checked by turning the range mark control fully clockwise. A bright spot will then rotate at the end of the trace line, around the edge of the PPI screen. If the circle drawn by this spot lies below the outer circle on the plastic scale, the calibration is correct. If the calibration is off, adjust the screwdriver adjustment, sweep length, which is underneath the indicator cover, until it conforms with the correct calibration.

OPERATIONAL TECHNIQUE

Preliminary operational adjustments.

Turn the azimuth mark increase clockwise, and set the position of the azimuth mark by operating the retard- indicator, antenna. If relative bearings are wanted, set the azimuth mark to 000 degrees; if true bearings are desired, set it to indicate the ship's heading at that moment. (Compass switch must be in compass position if true bearings are to be read.) Turn the azimuth mark low, but visible.

With the rec. gain turned completely CCW, adjust the screwdriver control on brilliance until trace barely appears. Increase rec. gain slightly until trace appears clearly, then adjust focus control until the trace is a sharp, distinct line. Then adjust the horizontal and vertical centering controls until the trace starts directly beneath the center of the amber shield over the screen.

Tuning the receiver.

Set the range selector switch as follows:

Tune the receiver, adjusting for maximum brightness

Set the mag.-conv. switch in the cony. position and adjust rec. tune control for maximum meter reading, from .4 to .8 milliamperes. Be sure to switch mag.-conv. back to mag., the proper position during operation. (Do not attempt to tune the receiver during the 15- to 30-minute warm-up period after turning on the equipment.)

Adjust receiver gain until "snow" appears in the background of the screen. This should be adjusted for the best target indications on tile PPI scope. If no targets are in the vicinity, adjust for noticeable amount of "snow."

Recommended operation.

The operator should check the tuning of the SL on taking over the watch. Tuning should not be attempted unless targets are available, or sea-return is present. Tuning is done by adjusting receiver tune control for maximum intensity.

Normal operation: use 25-mile scale primarily, with gain set so that background noise ("snow") is visible, but not bright enough to obscure indications. Search on the 25-mile scale for about four minutes, then search for about 30 seconds on the 60-mile scale, readjusting receiver gain slightly, if necessary, and paying particular attention to the longer ranges. After about 30 seconds on the 60-mile scale, switch to the 5-mile scale, and readjust the receiver gain if necessary. This is the scale on which the operator will detect small objects, close aboard, such as submarines awash. Report all contacts.

Station keeping: if radar information is needed for station keeping, the receiver gain should be reduced sufficiently to show ships in formation clearly. Do this immediately after completing the 30-second search on the 5-mile scale, then switch to the 25-mile scale, and repeat the cycle.

Submarine contact: after sound contact has been made with a submarine, or when such contact is probable, you should operate primarily on the 5-mile scale, with the gain sufficient to bring out some background noise. (Remember, unless the gain is up, small targets will not be seen.) Look for a short,

Surface contact: operation after contact with the surface target is made, including surfaced submarines or submarines awash.

The recorder shall call "stand by" five seconds before "mark" is called. If a single target is being tracked, "mark" should be called every minute (unless the 60-mile scale is being used, then "marks" are given every two minutes). If two targets are being tracked, one should be called on the minute, and the other on the half-minute, thus each target is "marked" at one minute intervals. Operators will call off bearing and range of target when "mark" is called.

If target is beyond the 5-mire range, but nearer than 25 miles, normal search routine should be followed, except for the reporting of targets every minute. A "mark" might be missed while searching on the 5-mile scale, but this is not serious, If "mark" is called while on the 60-mile scale, the operator may call the bearing and ranges from that scale. This point however, should not be used in determining course or speed.

If the target is within a range of 5 miles, search should be continued on the 5-mile scale primarily, switching to the 25-mile and 60-mile scales for 30 seconds each after 4 minutes on the 5-mile scale. Possibility of contact with other units must not be overlooked.

If the target is first detected at a range greater than 25 miles, the 60-mile scale should be used primarily, until the target has closed to within 25 miles, Search for four minutes on the 60-mile scale, then switch to the 25-mile scale, for about 30 seconds, and the 5-mile scale for about 30 seconds. Recorder should call "stand by," followed by "mark," every too minutes while reading from the 60-mile scale.

Clouds: echoes from clouds are often seen on the radar screen. Operators usually can recognize these as such, because of their distinctive appearance. Occasionally, however, this distinction cannot he made, and the cloud echo will resemble a ship echo closely. The operator should report them in either case, giving all information he can.

Jamming is deliberate interference, caused by the enemy, which limits the effectiveness of your radar; or it is interference produced by our ships to limit the effectiveness of enemy radars. There are several types of jamming, but all are characterized by some strong form of interference pattern on the indicator. These interfering signals are directional in nature, and the bearing or bearings from which they come, can be easily found by looking down the center of the lamming pattern. The jammer does make it difficult or impossible to read range, but effective jamming is not easy for the enemy to accomplish, and it is apt to disappear momentarily from time to time. Learn to expect it, and be prepared to follow the best course of action when the time comes. Do not mistake interference created aboard your own ship, or trouble in the radar set for jamming, the real thing will be directional, and its true bearing will not change immediately when your own ship changes course.

As you approach the jammer, the radar echoes from the jamming ship (if it is sea-borne) will increase in strength more rapidly than the jamming signal, and you stand a good chance of being able to read range through the interference. See part 3, Defense Against Jamming and Deception.

When jamming occurs:

PERFORMANCE

Maximum reliable range.

The higher the antenna, the greater the maximum range; for this reason, performance figures are given on the following page for several antenna heights.

The average minimum range for ship targets is about 500 yards (1/4 mile), and on aircraft targets about 700-1,000 yards. These figures will be somewhat higher when sea-return is strong.

Range accuracy.

The figures for the possible error of the set, plus the probable error of estimation are approximately:

Bearing accuracy.

Approximately +/- 2 degrees - 3 degrees

TROUBLES

Inferior performance of the SL radar can be recognized by the operator paying close attention to the indicator screen, the mag., cony. current meter, and by listening to the 800-cycle note of the spark gap keyer.

If the set is not tuned properly, targets will not appear on the screen with their usual intensity. Consequently, targets may approach your Ship considerably nearer than usual before they are first detected. Sea-return may he dimmer, and more reduced in area than you would expect, considering the condition of the sea. In general, echoes look normal except that they appear weaker than usual or reduced in size. You should try retuning the receiver whenever you observe

Sometimes, echoes will look scalloped, and the "snow" will appear in fan-like streaks radiating straight out from the center of the screen. When this occurs, it is an indication that the set is being keyed improperly; the technician should cheek the spark wheel electrodes. This trouble will also he revealed by a spitting noise, or an unsteady whistling from the modulator unit.

If the modulator whistles normally and the converter current is normal, but the magnetron current reads zero, either the pulse cable or the pulse transformer is faulty, and the technician should be notified immediately. No echoes will appear on the scope until the failure is corrected. When the bright spot of the transmitted pulse appears on the scope along with some "snow," but no echoes appear, check both magnetron current and converter current for normal readings. If they are working properly, a receiver rube is probably faulty; ask the technician to replace it.

If the equipment is set to indicate true bearings, and the azimuth mark does not change bearing when the ship changes course, the gyro compass may not be functioning. This fault may also be indicated by drifting of the azimuth mark and target indications on the screen. If the fault is not with the gyro, the trouble may arise from a slipping clutch. If the gyro compass is not functioning, you should request permission to switch to relative bearing, and do so by snapping the control switch (compass on-off), beneath the indicator panel, to OFF, and by setting the azimuth mark to 000 degrees.

SO RADAR

1. Off-on: this switch controls line voltage to the motor starting relays, blower, protective solenoid, and synchro phasing relay circuit. This switch is not used on the SO-1 and SO-2 radars. A separate bulkhead switch (18) is mounted near the plan position indicator to be used instead of 1.

2. N E: this is a normal-emergency switch which will be in the N or normal position during ordinary operation. There is a protective thermostat in the transmitter unit, which will turn the transmitter off if its temperature gets high enough to cause possible damage. If this should happen at a time when the radar must be used in spite of possible damage to the equipment, it can be started again by keeping the start button (4) pressed while turning the N E switch (2) to E, the emergency position. If the stop button (4) or the off-on switch (1) or the bulkhead stop button (18 used with SO-1, SO-2, SO-8) should be operated, the set will be turned off and high voltage can not be applied again until the N E switch (2) is returned to N, and the procedure for emergency operation described above is repeated.

3. Pilot: adjusts the illumination of the bearing scale around the PPI tube (9).

4. Start stop: controls the application of high voltage to the transmitter. (Do not confuse this with the bulkhead start stop switch used with SO-1, SO-2, SO-8.)

6. S W L: a screw driver control of sweep length. Sweep length may be varied to show a minimum of three range circles, and a maximum of six range circles.

7. Range selector switch: the scales are 5, 20, and 75 nautical miles on the SO and SO-A, with 1, 4, and 15-mile intervals between range circles on the respective scales, The SO-1, SO-2, SO-7, and SO-8 have range scales of 4, 20 and 80 nautical miles, with 1 mile between the circles on the 4-mile range, 5 miles between the circles on the 20-mile range, and 20 miles between the circles on the 80-mile range.

8. INT: this is the PPT intensity control for adjusting the brightness of the sweep and the range circles.

9. The PPI (plan position indicator) tube.

10. The Cursor: by means of this the relative bearings of contacts are read.

11. CCW off CW: this is the antenna rotation toggle switch. When in the CCW position the antenna goes counterclockwise automatically at 12 rpm. In the CW position it goes clockwise at 12 rpm. There is no provision for manual rotation.

12. Focus: used to focus the PPI tube for maximum definition.

13. Center: this control positions the start of the sweep. The sweep can be made to start from

14. Tune: this is the fine tuning adjustment. When it is adjusted for maximum echo brightness, the receiver will be tuned to the transmitter.

15. Marks: controls the intensity of the range marking circles on the PPI.

16. Gain: corresponds to the volume control on any radio receiver, it controls the sensitivity of the receiver.

17. Tune set: a rough tuning adjustment. It tunes the receiver approximately to the transmitter. It is adjusted for maximum echo, while the tune control (14) is in the mid-position. This is a semi-permanent adjustment.

18. Bulkhead stop start switch, used with SO-1, SO-2, SO-8.

TURNING ON AND OFF

Turning on.

1. Operate NE switch (2) to N. marks counterclockwise, pilot counterclockwise.

2. Be sure INT (8) is turned full counterclockwise; this is done to prevent burning on PPI.

3. Turn off-on switch (1) to ON if an SO. Press start button (18) on SO-1; dial light will come on when turned up.

4. The blower in the transmitter will be heard to start.

5. After two or three minutes, press start button (4), a relay will be heard to click, and the 400-cycle hum will be distinguished.

6. Turn INT (8) clockwise until the trace on the PPI can be seen with moderate intensity. It is possible to burn the PPI if the trace intensity is too high.

7. Adjust focus (12) for sharpness of sweep trace on PPT.

8. Operate CCW off CW switch (ii) to either CCW or CW, and the trace will rotate on the PPI at 12 rpm automatically.

9. Set the range switch (7) to the range on which

10. Turn gain (16) completely clockwise.

11. Adjust tune (14) until contacts or sea-return (echoes from waves nearing your ship) can be seen on the PPI indicator.

12. Stop the antenna on the best contact and adjust tune (1-1) for maximum brightness. If it fails to respond, set tune (14) to mid-position and adjust tune set (17) for maximum brightness; then make final adjustment with tune control (14). Tune set (17) is the rough tuning control, and tune (14) is the fine tuning control.

13. With switch 11, start the antenna in automatic rotation again in either direction.

14. Using center control (13) adjust the sweep trace so that the origin is almost in the center of the PPI scope. A small, dark circle, about 1/16-inch in diameter, should be seen at the center of the PPI to assure us that the sweep is not overlapping the center point.

15. Turn marks clockwise until range-mark circles appear on the PPI, and adjust SW-L (16) until 5 range circles show on the SO, or 4 range circles on the SO-1.

10, Note that no calibration is necessary. The set is permanently calibrated at the factory.

Turning off.

1. Operate CCW off CW switch to OFF.

2. Turn INT (PPI intensity control, 8) completely counterclockwise.

3. Turn marks (15) completely counterclockwise.

4. Turn pilot (3) completely counterclockwise.

5. Push stop switch (4).

6. Turn off-on switch (1) to OFF if set is an SO; push bulkhead stop button (18) if set is an SO-1, SO-2, or SO-8, and hold it down several seconds.

Adjusting the echo box.

The echo box furnishes an artificial echo or contact on the PPI indicator, to be used in tuning the receiver when no other radar targets can be found. It can also be used to determine if the transmitter is functioning. Adjustment is made as follows:

1. Put the operate lever in a horizontal position. (See illustration of echo box, fig. 4 SO-1.)

2. With the radar operating, stop the antenna on the bearing of the echo box pick-up antenna; this will be either 000 degrees, or 180 degrees,

3. Put the range switch (7) in short range position. The artificial echo should be seen extending out a mile or two when the receiver is tuned. You may use this echo to tune on, just as you would tune on any echo. Any decrease in sensitivity of the radar will be indicated by a decrease in the range extent of the false echo. On some sets, the echo extends in all directions.

4. To detune the echo box when not in use, pull the operate lever into a vertical position.

OPERATIONAL TECHNIQUE

Reading ranges.

Ranges are read by turning marks control (15) clockwise, until the range mark circles arc dimly visible on the PPI. The range circles are to he interpreted according to instructions already given in the section on Controls (7). Ranges must be read by estimation unless the contact happens to lie on a circle. Estimation of range is easiest and most accurate when using the short range scale, becoming more approximate as the length of scale increases. When the contact can be read on short scale, its range can be determined to within about 500 yards or a quarter of a mile. The medium range scale can be read with practice to a half-mile, and the long range scale to within about 1 1/2 miles. When not reading ranges, keep the range mark circles off the PPI since they may obscure weak contacts.

Reading bearings.

The bearings blade or cursor should be rotated by turning the bearing crank until it bisects the arc formed by the contact. Unless the operator's eye is in the plane of the blade-shaped cursor, a parallax error will result. His eye should therefore see the cursor as a fine line, which is adjusted carefully to the center of the contact. Proper use of the cursor will result in superior bearing accuracy.

When the cursor has been set, turn pilot control (3) clockwise until the relative bearing scale is illuminated sufficiently so that the bearing can be read. When not reading bearings, keep the pilot (dial light control) secured in a counterclockwise position, since the light from the bearing scale destroys the contrast

If you are yawing considerably on your course (as will often be the case on a PT boat), the relative bearing of contacts will be continually increasing and decreasing. For the same reason, contacts on the PPI will broaden into an ill-defined smear when yawing is excessive. If your own ship is steady on its course, bearing accuracy can be as good as +/- 2 degrees or +/- 3 degrees.

When taking bearings of close in targets which appear near the center of the PPI even on short range scale, and with SW-L (6) set for full expansion, it will be found helpful to use center control (13) to de-center the sweep trace, and move the contact out to a more convenient position on the scope.

If the contact is weak, and intensifies only once in several sweeps of the antenna, or if the bearing rate of change is high, it will be found helpful to operate CCW off OW switch (11), so that the antenna moves back and forth over the target instead of making full revolutions. Do not make this sector sweep less than approximately 90 degrees.

Long and short range search.

When long range detection is desired, put the range switch (7) in this position, use full receiver gain (gain full clockwise), and be certain that the receiver tuning control (14) is precisely adjusted. The maximum range at which targets can he detected increases with the size of the target and its presentment. For large ships, the maximum range will be about the same as the line-of-sight distance from the antenna, and can be approximated by the formula d = 1.2 (square root(HA) +square root(HT)); where d is distance in nautical miles, HA is your antenna or eye height in feet above water, and HT is the greatest height of the target above the sea.

If you did not expect to detect even the largest ship beyond 20 miles because your own antenna is low, you should use your medium range scale for long range search and adjust it to show 6 range-mark circles, using SW-L control (6). Under these conditions, you would be able to read ranges much more accurately, and therefore could get a course and speed solution more quickly (from your plot), than if you used long range scale. The formula above will not hold true for small ships or wooden ships since such craft do not reflect enough echo to be detected at maximum line-of-sight distance.

Short range search may he used to detect nearby submarines (if partly or completely surfaced), navigation buoys, small objects in general, and for station

If ships in your convoy or task force, are on stations inside your normal sea-return area, make periodic short range sweeps with the low gain, to see that they are not dangerously close or possibly on a collision course. A ship on a collision course will move down a radial line on the PPI. If a ship is going to execute a maneuver which will bring him close to you, put your cursor on him, if he moves straight down the cursor toward the center of the PPI, something has gone wrong and he is on a collision course with your ship.

False contacts and how they look.

Rain clouds: wide in bearing, deep in range, not sharply defined, with course and speed same as wind.

Ionized clouds: not visible to the eye, not easy to identify, often in groups, the course and speed same as wind, upper air will not always move with surface wind.

Floating objects (barrels, cans, etc.) small contact considering the short range, no course or speed.

Double range echoes: caused when returning echo is reflected from own ship, and makes a second round trip to the target, usually seen only when a large ship is close and on a parallel course. Will appear on the same bearing as a large ship, and at twice the range, its range rate will be twice the range rate of the large ship.

Reflection contacts: caused by your own radiated waves being deflected by some object aboard your ship, or another ship, in such a way as to cause a legitimate

Wakes: always appear as a small contact astern of some nearby ship; they vary in size, becoming largest when the target ship is in a turn.

Whitecaps to windward: sometimes, a contact will he seen just beyond the sea-return area in the direction from which the wind is coming. It will keep the same relative position regardless of course and speed of your ship.

Side lobe contacts: rarely give trouble, but may be seen when good radar targets are at close range. They appear at the same range as some target that is giving a good contact, and come in pairs, one on each side of the true target contact. They are smaller than the true contact, and smaller than might be expected at that range. Operating the set near high mountains may give side lobe contacts, which will be large smudgy contacts on the PPI scope.

Second sweep echoes: you may hear of these, but you will never see one on the SO radar, because their repetition rate is low enough to preclude this possibility.

PPI interpretation.

The radar beam is projected into space in much the same manner as light from a searchlight, and there are radar shadows similar to ordinary shadows. Radar can not "see" through mountains, or behind them, or through any other large obstruction; it cannot see around corners, whether they be formed by headlands or the horizon. For this reason, radar shadows show as dark areas behind high points of land, and in the position of low lying land. Visualize the light and shadow detail presented to an observer looking down from a high position in the sky just at sunset. The lighted areas would be light areas on the PPI scope of a radar, bearing in the direction of the sun from the island, and the shadow areas would be dark as you visualize them, You can now see why topographical details of a region help you recognize land features as they appear on the radar. Without these details you cannot fully interpret the picture.

Because of beam width distortion, all targets give pips which spread to the left and right of their correct bearing. Thus all targets seem wider than they actually are. A good finite target, for example, will cause a contact 15 degrees or more in width in a typical

Distortion of the beam width affects radar's portrayal of a coast line. If your beam strikes the coast at right angles, there will be no coast line distortion at that point, but the smaller the angle between the coast line and the radar beam (in horizontal plane, of course), the more the land seems to come out to meet you. This spread tends to reach a maximum at the points of left and right tangency established from the radar observers position. In other words, if you were off a coast line as straight as a ruler, your radar would show it as a slightly crescent-shaped shore line.

Since all targets spread considerably in bearing, and incidentally to some extent in range, ships may succeed in concealing themselves from radar by getting as close to shore as possible. Their contacts will then either be obliterated by the land contacts, or they will merge and appear as part of the land mass. Chances of escaping detection will be maximum alongside a high island, and at points of tangency established from the radar observer's probable position.

Special use of SO radar by PT's.

Due to yawing of the PT boat on its course, the relative bearing of all contacts will vary somewhat from one instant to the next. When a torpedo attack is made by full radar control, the accuracy of radar bearings will depend not only on the radar operator, but also on the helmsman's ability to keep the boat on a steady course.

Some PT's draw relative movement lines on the face of their PPI's, and maneuver during the approach so that the target contact comes down one of the lines to one of the range circles. This is done to establish the course of the target without having to plot it, and to reach a definite optimum position for firing torpedoes. When using a relative movement line on the PPI for target course determination, adjust center control (13) so that the sweep origin is at the center of the PPI. De-centering the sweep, while useful in getting bearings of nearby objects, introduces distortion, so that the picture is no longer a true plan position view, and ships on a straight course will not move in a straight line on the scope. In the final stage of this approach, the relative bearing of the target may be changing as much as two degrees per revolution of the antenna. When the

Piloting by radar.

This type of radar navigation may give fixes that are approximate, and fixes that are as accurate as the set itself (plus or minus 2* and plus or minus 500 yards), depending on the features of land. If prominent, finite radar targets, such as peninsulas, river mouths, buoys, large rocks offshore, buildings, lighthouses, and radio towers can be identified on the PPI scope, the best type of radar fix is possible. Under these conditions it is possible to determine set and drift due to current, by comparing dead reckoning with successive radar fixes. Otherwise, the position must be approximated by cutting in on mountain peaks, using left and right land tangents, using "range off" lines of position, and by plotting ranges to shore for about every 10 degrees on a transparent overlay, and fitting it to shore-line contours of a chart. These data can be used to good advantage in conjunction with those secured by use of the pelorus and fathometer. If the position must be approximated, it should be estimated by all possible methods and agreements looked for.

Tangents on land are not reliable because of two sources of error. In the first place, beam width distortion makes the land appear wider to the radar; therefore, left tangents tend to be small, and right tangents large. In the second place, radar often ignores low lying or sloping land, so that there may be doubt as to whether the radar is showing the land tangent or some other point inland. This introduces a tendency to carry tangent bearings inland, making the left one too large and the right one too small. These two sources of error offset one another to some extent varying with different types of terrain. Use every opportunity to compare radar tangents with pelorus tangents, so that you know the magnitude and direction of its error on various types of land.

Beware of radar's range off shore, because here again, it may ignore low lying land and indicate that you are farther off shore than you actually are. If the land is precipitous, radar will give your range off shore within the limits of the set's accuracy.

Do not rely on radar to pick up reefs or shoal water. These constitute low lying, poor radar targets, and will be detected at dangerously close range or else not at all.

When close to shore or entering a harbor, it will be found that land details can often be found by reducing receiver gain (turn gain control 16 counterclockwise). This tends to minimize beam-width distortion and sea-return. Remember, when studying details of land or entering a harbor, use low gain.

Jamming.

Jamming is deliberate interference, caused by the enemy, which limits the effectiveness of your radar, or interference produced by our ships to limit the effectiveness of enemy radars. There are several types of jamming, but all are characterized by some form of strong interference pattern in a given sector on the indicator. These interfering signals are directional in nature, and the bearing or bearings from which they come can be easily found by adjusting the cursor to the center of the jamming pattern. The jammer does make it difficult or impossible to read range, but effective jamming is not easy for the enemy to accomplish, and it is apt to disappear momentarily from time to time. Learn to expect it, and he prepared to follow the best course of action when the time comes. Do not mistake interference created aboard your own ship or trouble in the radar set for jamming, the real thing will be directional, and its true bearing will not change immediately when your own ship changes course.

As you approach the jammer, the radar echoes from the jamming ship (if it is sea-borne) will increase in strength more rapidly than the jamming signal, and you stand a good chance of being able to read range through the interference. See Part 3, Defense Against Jamming and Deception.

When jamming occurs:

1. Get the bearing and report it.

2. Keep operating the set and trying to read ranges through the interference. Try various settings of gain control (16). There is a chance the jamming will stop long enough for you to get range.

3. Keep reporting its bearing periodically.

4. Be ready to turn on a radar which operates on a different frequency band if ordered, providing you have one.

PERFORMANCE

Maximum reliable range.

The maximum reliable range depends mainly upon the antenna height. The higher the antenna, the greater the range of detection of ships, due to the line-of-sight nature of the radiation. The figures given below are for an antenna height of 17 feet. Insufficient data is available at present for performance at higher antenna heights, but comparisons indicate that maximum range performance is roughly comparable to that of the SG radar.

Antenna 17 feet

Minimum range.

Range accuracy.

The possible errors of the set may add to the probable errors of estimation, so that the following figures result for contacts that are not exactly on a range circle.

Bearing accuracy.

+/- 2 degrees for SO. SO-A, SO-1, SO-2, SO-8 provided your own ship is not yawing on its course.

TROUBLES

Reports from forces afloat indicate operational difficulties caused by moisture getting into the equipment. The transmitter-receiver, and PPI unit of the SO series radars are mounted in watertight cases, and sylica

The instruction hook requests that the dehydrator plugs he changed when they have turned from deep blue when dry, to light pink after they have absorbed

Abnormally high temperature in the transmitter-receiver unit, due to blower failure or some other cause, will turn off the high voltage automatically. It cannot be turned on again by the usual method. If it is necessary to operate the set in spite of probable damage to it, proceed as described under N E control in the section on Controls.

SF RADAR

SF RADAR

1. "A" indicator: used to identify targets at extreme ranges, for studying composition of echoes, and for accurate ranges.

2. Range scale: read the one that is illuminated.

3. PPI indicator: used to show tactical situations, for station keeping, and the most watched "scope" during general search. It is surrounded by a relative bearing scale.

4. Range knob: moves the range step on the "A" scope, and the range circle on the PPI scope when getting range.

5. Cal synch: a semi-permanent adjustment made by the technician.

6. "A" scope intensity: controls the brightness of the picture.

7. "A" scope focus: controls the clarity or sharpness of definition of the "A" scope picture.

8. 16,000-yard set: used in calibrating 16,000-yard

9. 16,000-yard range set: used in calibrating the 16,000-yard range, and to put the seventh range mark on the step.

10. 48,000-yard range set: used in calibrating the 48,000-yard range, and to put the 20th range mark on the step.

11. 48,000-yard zero set: used in calibrating the 48,000-yard range, and to put the first range mark on the step; first range mark represents 2,000 yards.

12. PPI focus: controls the clarity or sharpness of definition of the PPI scope picture.

13. PPI intensity: controls the brightness of the picture on the PPI indicator.

14. Calibrate-operate switch: when in calibrate position, range marks appear on the two scopes for

16. Green tuning eye: intended to be a tuning aid, but its use is not recommended.

17. Rec-gain control: adjusts the sensitivity of the receiver; it controls the height of the echoes and the grass.

18. Stop-start buttons: for turning set off and on. 19. Range switch: selects either the 16,000-yard or 48,000-yard scale,

Figure 4 SF-2. Transmitter unit.

20. Lo-tunning: this tunes the receiver to the transmitter; it is adjusted to give maximum pip height. This is an extremely critical adjustment, and the one on which the ability of the set to detect targets chiefly depends.

21. IFF gain: to be turned clockwise when interrogating with identification equipment. This is inoperative unless BL or its equivalent is used in conjunction with the SF radar.

22. Warning-training error: a light which indicates that the antenna (and consequently the target) is not on the indicated bearing. When lighted, it tells us that the antenna training equipment is out of commission and bearings will be wrong until repairs are made.

23. Antenna train control: when pushed in, the antenna can be trained by hand; when pulled out, the antenna will rotate automatically.

24. IFF on-off switch: when BL or its equivalent is connected to the SF radar, this switch is used to interrogate a desired contact.

Turning on.

Assuming ship's power is on and adjusted to 115 volts DC:

1. Press the black start button (18), on the receiver-indicator. In about 30 seconds, the pilot lamps will illuminate the range scale (2). See that PPI intensity (13) is counterclockwise.

2. Be sure the training control (23) is pushed in for manual operation.

3. After two and one-half to three minutes, the transmitter will automatically go into operation. If you are close to it you can hear the blower motors go on at this time.

4. Look at the meter on the transmitter unit. Set the toggle switch near the meter to MAG and the current should be five to six milliamperes.

5. Set the same toggle on CRYSTAL, and the meter should read between 0.2 and 0.6 milliamperes, if not, the lo-tuning (20) is probably off adjustment. (This is to be discussed later.) Full scale deflection represents 1.0 milliampere.

Turning off.

1. Push the red button marked stop (18 on the receiver-indicator unit).

2. Turn PPI intensity (13) down (counterclockwise).

3. Push in the training control (23) to manual the operation position.

CALIBRATION

16,000-yard scale (at the receiver-indicator unit )

1- Throw calibrate-operate (14) toggle on the receiver-indicator unit to CALIBRATE position.

2. Turn PPI (plan position indicator) intensity control (13) located near the right-hand indicator down to secure PPI during calibration. This prevents burning of its florescent screen during a prolonged period of calibration.

3. Adjust intensity of the "A" scope trace with the "A" scope intensity control (6), located under the left-hand indicator. Do not make it unnecessarily bright.

4. Adjust the focus knob, located under the left-hand indicator, until the "A" scope trace is sharp and clear.

5. Set the 16,000-48,000-yard range selector switch (19), located on the lower left side of the center to the 16,000-yard scale.

7. Adjust 16,000-yard zero set (8), located on the lower left side of the range knob, with a screwdriver until the trace looks like figure 4 SF-3. That is, until the first range mark is on the edge of the step as illustrated. The right side of the first range mark, makes an almost straight line from its peak to the bottom of the step.

Figure 4 SF-3. Pattern for calibrating 2,000-yard range an 16,000-yard scale.

8. Now set the range dial to read 13.75 on the lower scale (13,750 yards).

9. Adjust the 16,000-yard range set (9), with a screw driver, so that the seventh range mark is on the upper edge of the step, as in figure 4 SF-4. Note, that the range marks represent 2,000-yard intervals on the scope. They may be regarded as artificially created pips at ranges of 1,750 yards (first), 3,750 yards (second), etc., the seventh being 13,750. Naturally, you want the seventh one to be on the range step when the range dial reads 13.75.

Figure 4 SF-4. Pattern for calibrating 14,000-yard range an 16,000-yard scale.

10. Again set the range dial to 1.75 and repeat step seven. Since adjustment of zero set and range set are interdependent, you must alternately repeat step seven and step nine until both adjustments are simultaneously correct.

48,000-yard scale.

Set the 16,000-48,000-yard selector switch (19) to the 48,000-yard range. You now see more range marks than before, since they appear closer

Figure 4 SF-5. Pattern far calibrating 2,000-yard range an 48,000-yard scale.

2. Set the range knob (4) to read 1.75 (1,750 yards) on the upper scale (2). Adjust the 48,000-yard zero set (11) to put the first range mark on the edge of the step. See figure 4 SF-5.

3. Set the range dial (2) to read 39.75 (39,750 yards). Adjust the 48,000-yard range set (10) to put the 20th range marks exactly on the step, since the 20th 2.000-yard range mark represents 39,750 yards. See figure 4 SF-6.

Figure 4 SF-6. Pattern far calibrating 40,000-yard range on 48,000-yard scale.

4. Now alternately repeat steps two and three until adjustments are simultaneously correct. The 48,000-yard range is now calibrated. It has been found that SF and SF-1 radars will have a constant range error of about 250 yards (low) if calibrated on 2,000 yards and 14,000 yards, or 2,000 yards and 40,000 yards rather than as shown above.

OPERATIONAL TECHNIQUE

Receiver-indicator adjustments.

1. Throw the calibrate-operate toggle (14) to OPERATE.

2. Turn up rec-gain (17), located in the lower-left-hand corner, until grass appearing on the sweep (25) is about 1/8-to-1/4-inch high. It will look like figure 4 SF-7.

Figure 4 SF-7. Normal grass height.

3. Push in the 10-tuning (20) knob to engage clutch drive and turn it slowly back and forth, at the same time watching for a cluster of pips to rise up at the left end of the sweep. These pips are echoes from waves near the ship, and are known as sea-return (see fig. 4 SF-8). Adjust the lo-tuning (20) until they rise to maximum height. If there are two or more settings

Figure 4 SF-8. Tuning for maximum echo.

4. Targets may be found now by training antenna with the train wheel (23), (located under the right-hand PPI indicator). Train on a ship or land target if possible.

5. Make the final adjustment of lo-tuning (20), by tuning for maximum height of the target pip.

6. Adjust the PPI intensity knob (13), located under the PPI indicator, so that the trace is just visible on the PPI with rec-gain (17) at minimum, turn completely counterclockwise.

7. Adjust the focus knob (12), located under the PPI indicator, for a clearly defined sweep.

8. Pull out on the antenna training knob (23), and the antenna will rotate automatically.

9. Adjust the rec-gain (17) for the best picture while watching the PPI. About 4-inch of grass is best if the PPI is to be watched. The PPI is now in operation.

Reading bearings.

As the antenna rotates, a pointer (bug) revolves around the PPI indicator (3) in synchronization with it. The pointer indicates the direction, relative to the ship's head, in which the antenna points. Consequently, it also indicates the relative bearing of the target. New targets cause arc-shaped marks to appear on the PPI (see fig. 4 SF-9). Where they appear depends on their relative bearing and their range. Your own ship is always at the center of the indicator: the farther a target is from you, the more distant it will be from the center of the indicator.

To get the relative bearing of a target, stop the sweep and bug near it by pushing in the antenna training wheel, and then train by hand until the sweep passes through the estimated center of the target echo. It may help to train back and forth on the target until the echo is well defined on the indicator screen, before trying to stop on the center of it. Having done this, read the relative bearing on the scale opposite the bug. It should be noted, that due to non-uniform

Figure 4 SF-9. Correct bearing setting.

Reading ranges.

The range of an object may be found by ether of two methods; the range circle method, or the step method.

The range circle method is quickest and most commonly used. Notice that a circle of light appears on the PPI. It can be made larger or smaller by turning the range knob. If the circle is made to pass through the target echo, the range of the target may then be read on the illuminated range scale. Notice also, that the upper range scale is illuminated automatically when the 16,000-48,000 switch is on 48,000 yards; the lower range scale is illuminated when on short range (16,000 yards), so there is little chance of reading the wrong scale.

The step method of getting range is more accurate; the "step" can be seen to move back and forth on the "A" type (left-hand) indicator as the range knob is turned. When the target pip is just at the upper edge of the step, as in figure 4 SF-10, the range of the target can be read on the illuminated range scale. Of course, it is necessary to stop the antenna on the target to get the range by this method.

Figure 4 SF-10. Position of step for correct ranging.

Special situations.

The operator should check calibration of both range scales, and the adjustment of the lo-tuning when he comes on watch.

General search. If he is standing a general search watch, the operator will spend most of his time on long range, using PPI and automatic antenna rotation, but making an occasional sweep at 1 rpm on manual control, watching the "A" indicator, Every five minutes it is a wise precaution to switch to 16,000 range scale and search in the sea-return area by reducing rec-gain (17).

Less gain will be required when using the "A" scope than when using the PPI. The gain is carried high when searching for targets at the maximum range of the set, i.e., enough gain to cause a snowy background on the PPI when it is being watched, or about 3/16-inch of grass on the "A" scope when using it. However, it will be turned lower when observing nearby objects.

False contacts. From time to time, false radar contacts will be made. Even with experience it is not always possible to tell with certainty when one has a false contact, so the operator should not fail to report a contact merely because he thinks it is false. These phonies may he caused by invisible ionized clouds, rain squalls, birds, white-caps to windward, small floating objects, and less common items. For further information, see the section on Pipology, Part 3.

Reporting. The operator should keep careful track of all visible contacts and watch especially for the sudden appearance or disappearance of echoes (strong indications of subs). He should also report all ships when they first become visible, report ships which may pass dangerously close, watch for ships on collision course (those whose bearing remains constant as the range closes), and make a routine report on first picking up land or losing it. Furthermore, it is a good policy to have the operator make some sort of routine report every five or ten minutes to the OOD, or

Fire-control. It is conceivable that SF radar may have to he used from time to time for fire-control. When this is done, train on the target, and stop the antenna there; get ranges by the range step method using the "A" indicator. Radar bearings should not be used unless there is no alternative, since the error may be + or - 2 degrees to 3 degrees, It is also possible to pick up the shell, splash and estimate the range error; to spot in range, stop on the target and watch the "A" scope. The shell pip looks like a mouse running under a sheet.

Navigation. Radar is a handy navigational aid when within range of land. It is important, though, to know when you can depend upon it and when you can not. Radar is apt to ignore low-lying land so that any attempt to get the range of a long sloping shore, or the tangent bearing on a section of land that rises gradually, would be unwise. Where land or buildings rise abruptly from the sea, the range to shore or a tangent bearing is easy to get. Mountain peaks and other prominent radar targets, are often identified by reducing rec-gain, since they will be the last targets seen as the gain is cut down. All targets on the PPI appear wider than they really are, due to the width of the beam of energy from the antenna. For this reason, tangent bearings may have to be taken inland a few degrees, the exact amount depending on the strength of the echo. Experience will improve this technique.

Since ranges are relatively accurate, range fixes on two positively identified, small, finite targets, are dependable.

When entering waters in which the PH picture is complicated by many strong land echoes (as in a harbor), it is necessary to reduce rec-gain to see the land-sea boundary, because of the blurring effect of the beam width distortion, and the obliterating effect of sea-return at close range.

Jamming and deception.

There is no doubt that the enemy considers our radar an extremely dangerous weapon, and consequently it is only reasonable to expect him to try every means possible to make it less effective. He may use two tactics to do this: jamming and/or deception. Every

When the enemy broadcasts radio signals, intending that our radar receive them, and they show a confusing pattern on the screen, it is called jamming. Use of dummy targets (tinfoil, kites, balloons, etc.) is called deception. Of course, more precise definitions are sometimes given, but these are satisfactory for this discussion.

The SF radar can he jammed, and it will show echoes from the tinfoil the enemy sometimes throws out to confuse the operator. The operator should no! become alarmed when either of these things happens.

If you were suddenly confronted with jamming, without previous experience, it would appear impossible to work through. However, it is not really that serious if the following procedure is carried out:

The first reason for obtaining a bearing on the jamming is to determine whether or not it could be accidental interference instead. Jamming will not only be directional, but its true bearing will not be changed by any sudden change in your ship's course. Interference originating aboard your own ship will either he non-directional and appear on all bearings, or else it will always be on some certain relative bearing regardless of your own ship's course.

Try moving the gain control up and down. This is probably one of the most important countermeasures than can be taken, and the one most commonly overlooked because of its simplicity.

In most cases, except when effective noise modulated jamming is being encountered, there is a setting of the gain control where it is possible to range on a target in the presence of heavy jamming. If there are several echoes on the same bearing, the best setting for each echo is different. Of course, it is more difficult to obtain these ranges because of the distortion of the echo produced by jamming, but it is possible to obtain the desired information. However, the extra effort is worth while, because the enemy would not he jamming unless he were trying to conceal something important.

Try changing the receiver local oscillator tuning. When you change the lo-tuning, you lose some of the height of the desired echo. However, if the jammer is not exactly on your radar frequency, there is a chance that you will detune the jamming signal more than the echo signal. Considerable improvement can sometimes be obtained this way. Try swinging the lo-tuning dial in both directions to see which direction makes the greatest improvement. Note the correct setting of the lo-dial, so that it can be returned to its normal position when no jamming is present, or if detuning does not help, otherwise the radar will not give optimum performance.

Even if the jamming is extremely effective, keep operating and do not turn your radar off. Turning your radar off informs the enemy that his jamming is effective, and certainly makes the radar completely worthless. The effectiveness of the jamming may change from time to time, so if you are persistent enough some information may be obtainable.

Report the nature and bearing of the jamming to CIC. Recognizing the type may be difficult because non-synchronous patterns sometimes appear blurred beyond recognition. Inasmuch as knowledge of jamming type* may possibly help identify the jammer in some cases, this information should be reported if possible. Above all, never turn off the radar.

When jamming and/or deception is encountered, full 360 degree search must be continued. However, the antenna should be stopped from time to time for short intervals, in order to try reading through the jamming, using the "A" scope. You also must be prepared for any diversionary tactics, for the enemy may or may not use jamming and 'or deception to divert your attention from the bearing of the main attacking forces. This problem is simplified somewhat when similar but separate radars are used for reading through jamming and for searching.

Maximum reliable range.

The maximum reliable range on various types of targets depends on the height of the antenna. The higher it is, the greater will be the maximum range of detection. This is especially true for large ship targets. The performance data below shows approximately what you can expect if your antenna is between 50 and 70 feet above the sea.

Minimum range.

The minimum range with all controls adjusted for shortest range detection will vary somewhat, depending on the roughness of the sea. A rough sea, means more sea-return interference and greater minimum range, especially on smaller targets. The figures below show approximately what to expect:

Minimum range.

The minimum range with all controls adjusted for shortest range detection will vary somewhat, depending on the roughness of the sea. A rough sea, means more sea-return interference and greater minimum range, especially on smaller targets. The figures below show approximately what to expect:

The range accuracy of this radar will be best when the ranges are read from the "A" scope using the step. The accuracy under these conditions is about +/- 200 yards, + 1.0% of the range. In other words, even when you calibrate correctly and read the range indicated by the range dial properly, your radar range may be off 400 yards on a target 20,000 yards away, or 600 yards on one 40,000 yards away, but only 220 yards on one 2,000 yards away.

Bearing accuracy.

Bearing accuracy will he best when the contact is strong and steady. By using manual antenna train, that is, stopping the sweep in the center of the contact seen on the PPI, a good operator will usually be within +/- 2 degrees of the correct bearing of such a target. If the contact is E-1*, and visible only periodically the error may rise to 3 degrees or 4 degrees.

TROUBLES

If for any reason the bug should fail to give the correct relative bearing of the antenna, the light near the train wheel, marked warning training error, will glow. The technician should be called if this light continues to glow, but an occasional intermittent flash will be of no consequence.

Gunfire or depth charging might possibly jar open relay K 201, which is located behind the front panel of the transmitter unit. If this happens, the transmitter will become inoperative for about 2 minutes, but will come on of its own accord at the end of that time.

SJ-a, SJ-1 RADAR

SJ-a, SJ-1 RADAR

Main control unit.

1. Main off and on switch: applies AC voltage to the SJ radar set.

2. Green light: when illuminated this indicates the main switch is on.

3. Load voltage meter: indicates the voltage applied to the radar set.

4. Load autotransformer: controls the voltage reading of 3.

5. Regulated rectifier voltage meter: indicates the DC voltage output of the regulated rectifiers.

6. Meter switch: positions 1 and 2, determines which regulated rectifier voltage is indicated on 5.

7. High voltage rectifier off-on switch.

8. Red light: indicates when the AC power is applied to the high voltage variac.

Figure 4 SJ-1. Main control unit.

9. High voltage variac: controls the DC output of the high voltage rectifier.

10. High voltage rectifier voltmeter: indicates the DC voltage applied to the transmitter-receiver unit.

11. High voltage rectifier current meter: indicates the current in the rectifier circuit.

13. Heater switch on-off: controls the AC plied to the heating elements in the range and transmitter-receiver unit.

14. Pilot lights: bright-dim switch.

Transmitter-receiver unit.

Figure 4 SJ-2. Transmitter-receiver unit.

1. Crystal current meter: reads 0.5 to 0.7 milliamperes when the equipment is properly tuned (this, however, is not the maximum crystal current reading obtainable).

2. Fine pulse rate control: will vary the pulse repetition rate from 1,300 to 1,700 pulses per second.

3. A.F.C. on-off switch: the automatic frequency control (automatic tuning circuit) will tune the receiver when ON, however, this circuit drifts and should be used only to check manual tuning.

4. Wave-guide transmission line to antenna.

Range-indicator unit.

1. Horizontal centering control: controls the position of the sweep or picture on the scope.

3. Lobe separation: determines the amount of separation of the pips when 2 is on.

4. Sweep control: determines the length of sweep on the scope.
(a) Main sweep: 0 to 60,000 yards.
(b) Expanded sweep: 0 to 20,000 yards.
(c) Precision sweep: 3,000 yards (1,500 yards each side of the range step).

Figure 4 SJ-3. Range-indicator unit.

5. IF gain: controls output of the receiver (determines height of grass and pips).

6. Focus control.

7. Lobe motor on-off switch: applies power to the lobing motor.

8. Intensity control: screwdriver adjustment, to be set by the technician.

9. Range zero knob: used to zero the sweep.

10. Receiver-tuning: tunes the receiver to the transmitter frequency.

11. Noise suppression: screwdriver adjustment, to be set by the technician.

12. Scope: cathode-ray tube.

PPI-indicator unit.

1. PPI cathode-ray tube.

2. Sweep selector switch: (8,000, 40,000, 80,000 yards range).

3. Scale light: azimuth circle.

4. Driving cable.

5. Video gain: screwdriver adjustment.

6. Focus: screwdriver adjustment.

7. Horizontal centering: screwdriver adjustment.

8. Vertical centering: screwdriver adjustment.

9. Range circle: adjusts intensity of the range dot.

10. Intensity: adjusts brilliance of the scope.

Range unit.

1. Dial light dimming switch.

2. Heating circuit indicator lamp.

3. Range counter dial.

4. Zero adjustment: to be adjusted by the technician.

5. Counter adjustment: to he adjusted by the technician.

6. Clutch adjustment: to be adjusted by the technician.

7. Range crank.

Figure 4 SJ-5. Range unit.

TURNING ON AND OFF

Open antenna wave guide valve and perform the following operations from the main control unit:

1. Turn on heater switch (13) 30 minutes before attempting to operate, if at sea, leave heater switch on at all times.

2. Turn on main switch (1), a green light will glow if set is operating correctly.

3. Check to see if blower motors can be heard in the transmitter-receiver unit, If not, turn the main switch off and call the technician.

4. Check the load voltage meter (3) for 120 volt reading. If this is not indicated, make adjustment of load variac control (4) for 120 volts.

5. Check regulated rectifier voltage meter (5) for 300 volts, check both positions of switch 6. If either one is off more than 15 volts, call the technician.

6. Turn on high voltage switch (7) 55 seconds after line switch was operated, a red lamp will light (8) if the high voltage switch is on. The high voltage should immediately jump to 0.9 and to 1.2 K.V.; providing the H.V. variac has been left at its proper setting when set was last secured.

7. The high voltage rectifier current meter (11) should read between 140 and 160 milliamperes.

8. Check the load voltage meter (3) again, for a value of 120 volts.

9. Turn on antenna control switch (12).

Turning off.

1. Turn off antenna control switch (12).

2. Turn off high voltage switch (7), do not reduce high voltage variac (9).

3. Turn off load voltage switch (1).

4. Do not turn off the heater switch (13) unless the set is to be worked on. Other units need not be touched.

CALIBRATION

Zero setting.

There has existed sonic uncertainty as to the proper zero set adjustment. In most cases there is no reference target available, whose range is known precisely enough to enable a satisfactory determination of zero set correction. Scribing ranges from charts is not generally satisfactory, because of shrinkage of

Where such a known range is not available, all SJ-1 equipment should use the counter setting of 99,940 for zero set. This number has been established by repeated observations over accurately surveyed ranges, and while it is subject to a possibly 10 yards variation among equipment, it should be used in preference to any but positively known local reference ranges.

One way of accurately determining a range, is by the use of double range echoes, (see Part 1, External Calibration). To do this, maneuver alongside a large ship at a range of 500 to 1,500 yards. When you train your antenna on this ship, two echoes should be seen; one at approximately the correct range, and a small double-range echo at approximately twice the correct range. Read these two ranges carefully and subtract the smaller from the larger-the difference is the actual range of the ship, regardless of whether your radar has been properly zeroed or not. Assuming this range is 800 yards, to find the exact zero set figure for your radar, you would proceed as follows: crank the range counter to exactly 800 yards and use the zero adj. knob to line up the target pip and step (use precision sweep during this operation). Now crank the range knob until the left edge of the transmitted pulse lines up with the step, and then read the range counter. It will probably read somewhere between 99,940 and 99,960 yards. Record the reading for future use in making the zero set adjustment. It is wise to avail yourself of every opportunity to check the zero set by means of double range echoes. If the double range echo appears at exactly twice the range of the true echo, you can be sure that the zero set adjustment is correct.

Under no circumstances should zero set be made with the counter at 00,000. This would increase all range readings by about 60 yards, and would go far toward defeating one of the main contributions of radar-accurate ranges.

The correction is required due to two factors: distance traveled from the transmitter to and from the antenna, and certain transmission delay and other effects within the equipment, such as build-up time in interstage filters.

Zero set procedure.

Torn on the set and tune properly.

3. Turn IF gain fully clockwise (5 on range indicator unit).

4. Set sweep selector switch on precision sweep (4 on range indicator unit).

5. By adjusting the set range zero knob, move the step to the right until the leading edge of the transmitter pulse meets the downward portion of the step, as shown in figure 4 SJ-6.

Figure 4 SJ-6. Transmitter pulse for proper zero set.

OPERATIONAL TECHNIQUES

Tuning the receiver (at range-indicator unit).

1. Check sweep switch (4) on all three positions to see if a sweep and step are present on the scope for each position. If any are missing, notify the technician.

2. Turn IF gain (5) fully counterclockwise; and adjust focus (6) for narrowest sweep or line possible.

3. With sweep switch (4) on expanded, rotate IF gain fully clockwise.

4. Adjust receiver tuning control (10) for maximum pip height on scope if pip is present. AFC switch (3) on transmitter-receiver unit must be off during this adjustment.

5. If pip height is saturated (pip has a flat top and not a sharp point), reduce IF gain (5) until pip is pointed, and make further adjustment of receiver tuning control (10) for maximum pip height.

6. Should no echo be present for use in tuning, put the sweep switch (4) on precision and the range dial at about zero. Tune for maximum indication of the wave echoes. If no wave echoes or other indications are available, the experienced operator can tune the set by noting: appearance of transmitter pulse on precision sweep, and reading of the crystal current meter on the transmitter unit. If an echo box is available, it can he used to put a

7. If targets are available, train on one, and turn on the AFC switch on the transmitter (3). If the automatic tuning circuit is working properly, and if manual tuning is correct, no change in echo height should occur. In any case, if echo height increases, the manual tuning is not correct.

Note: The AFC circuit should be used only to check manual tuning.

8. Adjust wave guide valve for maximum tuning or echo height.

9. Never use receiver tuning control (10) to decrease pip height. Always use IF gain control (5).

Adjusting PPI intensity. It is to be noted, that this control must he set precisely, and not varied to suit personal preferences and lighting conditions. Adjust intensity (10 PPI unit) until the sweep trace is just visible on the scope, when the IF gain (5 on range indicator) is set at minimum.

Any light which shows, with no signals or noise present, will impair the usefulness of the indicator by reducing the contrast of the pattern, that is, echoes will not stand out clearly nor be distinguishable from noise.

The intensity should not be turned too low, because then, unless special care is taken, weak signals will not be able to excite the screen sufficiently to be detectable.

Drift in tuning during warm-up. When the system is turned on, after a considerable period of shut-down, at least 5 to 10 minutes is required for the beat-oscillator in the receiver to reach final, stable, operating temperature. This period can be reduced to about two minutes by applying line voltage to the SJ-1 at least 10 minutes before surfacing, and by opening the antenna wave-guide valve. High voltage maybe applied before the antenna breaks surface and tuning checked approximately, by the appearance of the transmitted pulse on the precision sweep, with the range crank at about 99,940 yards. Zero setting of the range step is also checked at this time. Use hand train of the antenna, and report to the Captain when the antenna is free of water. Immediately check tuning on sea-return (wave pips), and make two complete 360 degree searches, reporting the results of each search. These searches should he made on expanded sweep. Continue to search with hand train of the antenna until surfacing is complete.

Reading bearing and range.

1. To obtain approximate bearing of the target, rotate the antenna crank back and forth (lobing

2. When an accurate bearing of the target is desired:

(a) Turn the lobe motor switch (7) on the range indicator unit on.

(b) Turn on the lobe separation knob (2) on the range indicator.

(c) Rotate lobe separation knob (3) clockwise, until two pips and two steps are present, as illustrated in figure 4 SJ-7.

Figure 4 SJ-7. Scope with and without lobing.

(d) Rotate antenna crank back and forth until the two echoes are at the same height.

(e) Read bearing dial for correct bearing of the target with respect to own ship-relative bearing.

3. To measure the range, first turn lobing switch (7) off; then rotate the range crank, which moves the step on the scope, until the step is approximately at the pip being measured.

4. Turn sweep switch to precision sweep.

5. Advance the step until the beginning of the pip sets exactly in the corner of the step as in figure 4 SJ-8.

Figure 4 SJ-8. Position for correct ranging.

6. When the pip is in the step correctly, the range of the target can be read from the range dial on the range unit.

It is suggested, that after adjusting trace separation correctly, that the lobe separation switch be left on at all times, and that the trace separation knob not be

Due to increased power output of SJ-a and SJ-1 radars, minor lobes present considerable trouble at close ranges; they can be easily located and avoided by use of the PPI scope. Echoes from minor lobes (side lobes) will disappear as receiver gain is decreased.

Bearings and ranges may he read approximately from the PPI scope without stopping the antenna. It is possible to obtain target course within 5 degrees, and target speed within 3 knots from this data. The following suggestions will speed the obtaining of data from the PPI and increase the accuracy:

Operation at short range.

Any radar antenna projects a small amount of energy in every direction. This can be visualized by comparison with a searchlight. There is a certain amount of illumination, even directly behind the light. In the case of SJ-1, the distribution is known, and is such that a very small amount is projected to the rear of the antenna. This is obviously extremely low, but since the sensitivity of the receiver is such that a signal will begin to show when the received energy is infinitesimally weak, it is not surprising that when the IF gain is set high, an echo will be received in practically a full circle, from a large target, at ranges of less than 2,000 yards. The only recourse in such a ease is to reduce the IF gain sufficiently to remove all but the main echo.

In a situation where this is done, it is well to use the time between taking data to turn up the gain, and to observe any other targets which may not be seen with the low gain setting required to resolve the short-range contact. It is stressed, that the IF gain must continually be adjusted to suit circumstances during any operation, except long-range search.

It will be found, that as range is closed, the arc subtended by an echo will increase. This is particularly evident on the PPI. There are two reasons for this: the angle subtended by the target will increase; and the echo will begin to show well before the antenna bears full on the target. Reducing the IF gain will

The following search routine is suggested for SJ-a and SJ-1 equipment: 360 degrees searches are to be made at all times; suggested antenna speeds are 6 rpm, or less, for PPI search, and 1/2 rpm for "A" scope search.

High gain indicates the most efficient receiver gain setting for long-range search. Low gain refers to the receiver gain sufficiently reduced to enable targets to be detected inside the sea-return area. Care must be taken not to reduce gain too much. It has been found that alternate PPI and A scope searching provides diversion for operators, thus relieving strain.

The following suggestions pertain to the tracking of targets:

If necessary, shift the antenna to power training for a 30-second interval every two or three minutes, to secure this auxiliary data. Complete search must be made at least every three minutes.

If provisions are not available for operation of IFF with SJ-a or SJ-1 radar, all questionable targets should be challenged by means of the SD radar's IFF system. Simply look for IFF response at the range of the surface target on the SD screen. See Part 2. General IFF Principles.

Pipology.

Clouds and rain squalls. These can frequently be detected at great ranges, and are not always easily identified. Usually, they will show on the PPI as being several degrees wider than normal ship echoes, depending on the extent of the cloud. They will frequently tend to look like landfalls, but can be distinguished from such, where certainty as to ship's location is lacking, by tracking to determine whether the target has course and speed as clouds have when driven by wind. Fluctuation of the echo is not necessarily an identification, because at long ranges land echoes sometimes fluctuate abnormally. Echoes from clouds are usually mushy, due to the absence of definite, reflecting planes.

Birds. Echoes from birds constitute a source of confusion to radar personnel. Birds in flight can usually be identified by their random courses and speeds, as well as by the fact, that, being so small, they will only show echoes at ranges within 2,000 yards. There should be no confusion between birds and aircraft, because the latter will show stronger echoes and will be seen at far greater ranges than the birds.

Ships. The approximate size of ships can be estimated by the maximum range of detection, the rapidity of the bobing motion, and in some cases the speed. The first two factors will be affected by the following:

Aircraft. The beam of the SJ-1 antenna, is directed toward the horizon, but low flying aircraft will frequently produce echoes. To recognize them, set the range mark on the echo, and watch for noticeably fast target motion. The PPI can also be used. The course of the aircraft might be such that range changes slowly, in which case, the PPI will indicate rapid change of bearing. It is important to realize, that echoes from aircraft will never zip across the screen, because so much range is compressed and displayed in the few inches of the screen. Even projectiles can be followed with ease. An airplane traveling at 200 mph, either directly toward, or away from the antenna, will require about 40 seconds to traverse the prec. sweep.

Minor lobes. It is characteristic of radar antennas, that some energy is projected in minor lobes or beams of energy, at some divergence from the main beam. In the case of SJ-1, the required small size of the antenna, as well as the necessarily massive construction of the projector head, accentuate the minor lobes. These are greatly reduced in power from the main lobe, but echoes will be received in response to minor lobes when the target is large, close, ad the IF gain is high. When present, minor lobe echoes will show at roughly 15 degrees divergence from the main echo, and at the same range as the main echo.

The presence of minor lobe echoes is easily observed on the PH. Since they are weak, compared to the main echo, they will not show on small or distant targets. Roughly, with the IF gain well up, minor lobe echoes may be expected from a destroyer at 3,000 to 6,000 yards. The nominal divergence of 15 degrees will vary among installations, and the minor lobes will seldom be alike in strength.

Where a group of targets, such as a convoy, is being viewed, echoes from minor lobes are confusing. The first recourse is to study the PPI pattern, for main and side echoes in characteristic groups, and to reduce the IF gain to where only the main echo from each group remains. Where the range is short, and the convoy is widely spread, this must be done judiciously in order not to lose real echoes from small targets, such as wooden escort vessels.

Jamming.

Since local interference or trouble may resemble jamming, an operator, after first reporting it, should perform these cheeks to see if the signals are from an outside source. Check whether the strength of interference varies as the antenna bearing is changed; or whether interference disappears when the antenna wave-guide valve is closed.

If interference is external and from another radar, it will consist of a definite series of equally strong pulses, consistent in width and spacing. These pips may move to the right or left on the screen (pulse spacing remaining constant), depending upon the pulse repetition rate of your radar and that of the interferer. Their speed of travel along the time base may be varied as your own pulse rate is varied. The interference will disappear when the wave-guide valve is closed. They are definitely effected by a variation of receiver tuning, and vary in strength as the antenna is rotated.

Note: All of the above points will appear on the PPI scope as bright spots, moving along the sweep (or as spirals from the center to the outer edge, if the antenna is rotating).

If the interference is external, and from an intentional jammer, it will generally conform to a known type of jamming signal, and may not be effective enough to prevent an operator from seeing targets in the jammed sector. It will also disappear when the wave-guide valve is closed. It will definitely vary as antenna bearing is changed, and due to the strength of the signal, it may burn a definite, brilliant sector on the PPI scope.

To read through jamming, concentrate on the "A" scope in the jammed sector; an experienced operator can spot a target on it most of the time. Do not neglect searching completely around 360 degrees. The effectiveness of a jammer, which is covering a target you are tracking, may be decreased by very slightly changing receiver tuning without losing your echo. Training the antenna slightly off the target, to one side or the other, may reduce the jamming more than the echo. Changing pulse repetition rate, or changing the high

A jammer must continually transmit at the radar frequency of your radar. You can slightly vary the frequency by varying high voltage, as described above. The corresponding correction on the part of the jammer, may allow a free operating interval.

Do not give up trying to read through a jamming signal, because as the range of a jammer closes (and the range of any accompanying target), the target echo will increase much faster in strength than the jamming signal. The higher the frequency of transmission, the harder the job of jamming, hence, the easier the task of evading or reading through. Enemy use of radar jamming in the Pacific has not been pronounced, but can be expected as soon as they can produce equipment which will do the job.

Mechanical jamming.

The Japs and the Germans have been known to use several types of radar deception. Window has been used in an attempt to hide aircraft. It consists of concentrations of reflecting material, which can be spread by dropping it from aircraft, or by firing it from a gun. It may also be used to mask ships. This material presents a numerous collection of pips, which may cover a wide sector; all pips fluctuate at a very rapid speed, and may appear quite similar to a cloud, though much stronger.

Echoes emanating from balloon bourne reflectors have been used to draw radars off of true targets. If you track these, their course will he that of the wind and one-half to two-thirds of the wind speed.

Diving procedure.

When the word "standby to dive" is passed, remove high voltage from the transmitter, and close the antenna wave-guide valve. Secure the rest of the set in a routine manner. The antenna should be secured on a 180 degrees bearing when not in use, especially while running on the surface.

PERFORMANCE

Maximum reliable range.

The range capability of a given installation is effected mainly by the following conditions:

Of these, the first three are entirely obvious. Concerning item (4), a slight degree of confusion is possible when attempting to judge the size of a target by the strength of an echo, because a large wooden ship will usually not produce an echo larger than a considerably smaller steel ship.

The effects of atmospheric conditions are comparatively obscure, but a few generalizations may be made. Fog causes occasional slight reduction in range. Heavy rain causes some reduction, but no cases are known of serious reduction due to rain. It seems well established, that in the North Temperate zone there is some daily cycle, whereby range capability of SJ-1 radar equipment, increases above normal in the late afternoon and early evening.

Antenna 33 Feet

Mountainous landfalls and freak conditions, can produce echoes under conditions which may lead to considerable confusion, if not fully understood. The maximum range displayed on the indicators is nominally 80,000 yards (PPI). However, echoes have been received many times from ranges so great, that the received echo does not arrive until the next succeeding sweep, or cycle of operation. Such second-sweep echoes, usually appear on the indicators at relatively short ranges, and can he misinterpreted as nearby targets. In the SJ-1, provided with variable pulse (recurrence) rate control, this type of false signal can quickly be identified by shifting the pulse rate control on the transmitter back and forth. This will cause any second-sweep echoes to move back and forth in range across the screen. Since this condition cannot be called rare, remember, the best protection against it is to understand the possibility, and the method of checking.

Minimum range.

The main source of bearing error, assuming accurate alignment of the bearing indicator, is play in the training gear. This is beyond the control of the ship's personnel, but operators can do much to overcome this play, by lobe-switching to match the pips carefully, and by then feeling for the ends of the backlash motion, and by holding the handwheel as near as possible to the middle of the free motion to read bearings. By this practice, bearings may be read very consistently with a maximum error of 1/4 degree on large steady pips. Range approximately, +/- 25 yards, + .1% of the indicated range.

Resolution.

Bearing: 5 degrees.
Range: 40 yards.

TROUBLES

There are two factors which can cause had bearing readings (other than minor lobe and extended close-in

It is recommended that each submarine make calibration runs, to provide tables or charts showing the bearing indicator corrections, for conditions of either or both periscopes raised, SD mast raised, and combinations of periscopes and SD mast. It is probable that the charts or tables for some combinations of SD mast and periscopes will he identical. Such information, posted at the operating position, will enable full accuracy to be obtained under all circumstances.

SD RADAR

Receiver-indicator.

1. Focus control: controls focus of the sweep.

2. Intensity control: controls brightness of the sweep.

3. Markers: allow markers to be put on the scope. Used for obtaining ranges of targets; use of IFF in extreme right position.

4. Centering: controls position of the sweep on scope-horizontal positioning.

5. Stand-by light: when illuminated indicates power switch is on.

6. Power switch on-off: controls AC power applied to the set.

7. Transmitter plate light (red): when illuminated indicates switch, No. 14, is on.

8. Oscillator control: tunes the receiver to the transmitter frequency.

9. Sensitivity control: volume control of the receiver, controls height of the grass and pips.

10. Fuse F-202-Fuse F-201: protection for the AC supply.

11. Scope: cathode-ray tube.

12. Transmitter plate current meter: reading determines setting of the high-voltage variac, No. 15.

14. Transmitter plate variac: controls the amount of DC voltage applied to plates of the transmitting tubes.

15. IFF gain control: varies amplitude of IFF signals appearing below the time base.

Transmitter.

1. Red pilot light: when illuminated, indicates that the power switch is on at the receiver-indicator unit.

2. Transmitter plate current meter: reads the same as meter No. 13 on the receiver-indicator unit.

3. Filament primary voltage meter: indicates voltage applied to the primary of the filament transformer, which supplies AC power to filaments of the transmitting tubes.

4. Filament control variac: controls the amount of voltage applied to the filament transformer.

5. Operation hour meter: registers the total number of hours the set has operated.

6. Emergency switch off-on: is in series with main power switch, to be used only in case of emergency.

8. Diplexer tuning control: varies the position of the condenser in the diplexer: to he set by radar technician.

9. Exhaust of blower: maintains cooling for the transmitter.

Figure 4 SD-2. Transmitter unit.

(Diplexer unit is to be adjusted by the radar technician only.)

Figure 4 SD-3. Antenna mast and diplexer, with most raised.

TURNING ON AND OFF

Turning an.

1. Check to see that the transmitter plate high voltage switch is off.

2. Turn on the power switch at the receiver-indicator.

3. Red pilot light on the transmitter should illuminate.

4. Check to see that the blower motor in the transmitter is operating.

5. Rotate the primary filament variac slowly clockwise, white watching the filament primary voltage meter increase to a value determined by the radar technician (110 to 120 volts).

6. At the receiver-indicator unit, check to see that the transmitter plate variac and the intensity control are fully counterclockwise.

7. Raise the antenna mast until the top insulators on the mast shoes are even with the top insulators of the diplexer shoes (see fig. 4 SD-3.)

8. Turn on the transmitter high voltage switch on the receiver-indicator unit. Check to see that the red pilot light on the receiver-indicator unit is illuminated.

9. If the line switch has been on for at least 30 seconds, proceed to turn transmitter plate variac clockwise until the plate current meter reads 8 milliamperes (or value specified by technician).

1. Turn the transmitter plate variac to zero.

2. Turn off the transmitter plate switch.

3. Turn off the power switch.

4. Do not touch other controls.

5. Lower the antenna mast.

Abbreviated procedure.

It is suggested that the following controls he left at the proper settings at all times, thus decreasing to a minimum the time required for tune-up:

(1) Filament control variac on the transmitter unit.

(2) Intensity, focus, tuning, sensitivity, and horizontal centering controls on the receiver-indicator unit.

Turning on is then reduced to the following procedure:

(1) Turn on the power switch on the receiver-indicator unit.

(2) Check the green pilot light on the receiver-indicator unit; blower motor in the transmitter, and the filament primary voltage meter on the transmitter.

(3) Raise the antenna mast as described above.

(4) Check to see that the transmitter plate variac on the receiver-indicator unit is at zero.

(5) Turn on the transmitter plate high voltage switch and increase the transmitter plate variac (if line switch has been on at least 30 seconds), until the plate current meter on the receiver-indicator unit reads 8 milliamperes (or as specified).

Use of the SD radar before surfacing.

1. The power switch should he on for 10 minutes before using the set.

2. Raise the antenna mast while at periscope depth.

3. When depth decreases to a point at which the antenna is clear of the water (7 to 10 feet), turn on the transmitter plate high voltage switch.

CALIBRATION

Use of markers for range measurement.

With the set properly on and tuned, turn the sensitivity control counterclockwise. Then turn the markers switch to the left, markers should appear on the screen. (Their appearance is illustrated in fig. 4 SD-4.) Place a strip of scotch tape across the screen,

Figure 4 SD-4. Range markers.

Return the marker switch to its normal position, and increase the sensitivity control to read target ranges from the tape. If this arrangement is used, care must be taken to switch markers on and check horizontal centering of sweep each time the set is turned on.

Range markers may he used directly for range measurement if desired.

OPERATIONAL TECHNIQUE

Tuning the equipment.

1. Increase the intensity control until the sweep is visible on the scope.

2. Adjust the, focus control for clearness.

3. With the sensitivity control near minimum (counterclockwise), rotate the oscillator control until a point of maximum response is noted on the scope (increase sensitivity control if necessary).

4. Adjust the sensitivity until the flag at the top of the transmitter pulse (left end of the sweep on the scope) is about 1-inch above the base line.

5. Adjust the oscillator control for maximum height of the flag. Now rotate the oscillator control through 360 degrees, checking for another tuning point which may increase the altitude of the flag. Leave the oscillator control on the best tuning point.

6. Increase the sensitivity control until grass appears on the screen. If a steady echo is present, cheek the oscillator tuning for the maximum echo

7. Re-check focus.

Figure 4 SD-5. Typical appearance of FLAG when properly tuned (sensitivity low).

The appearance of the flag at the top of the pulse (left end of the screen) will vary in different sets. Become familiar with the appearance of this flag when properly tuned, and tune for maximum height as well as proper appearance.

If the sweep does not appear immediately on the scope, turn the variac back to zero, and make successive attempts to increase it until a sweep is obtained. The sweep may jump and appear unsteady until water has drained from the antenna, this will cause no damage.

If the depth of the submarine increases to a point where waves may strike the antenna, arcing will occur at the antenna and possibly in the transmitter. Turn the transmitter plate variac to zero if there is a possibility that the antenna will become submerged, and then wait until the proper depth is reached. Quickly check the tuning and range markers, and make reports to the Captain.

It is important in this connection that controls and adjustments on the receiver-indicator unit be left untouched while submerged. A check of over-all tuning must he made as quickly as possible during the surfacing procedure.

Air search during surface cruising.

Watches of a half-hour duration should be adopted whenever possible. Only those men who have had previous SD radar experience, if available, should be

Report all targets and IFF signals, giving their ranges. Identify the composition of targets, using the following characteristics as a guide to your interpretation of target pips.

Report any unfamiliar signal or disturbance appearing on the screen. The OOD will immediately call the radar officer or technician to check this interference. Internal interference may come from any AC equipment aboard. External interference may represent jamming or other radar signals.

Caution: When jamming, or other radar interference is encountered, it is likely that your position, or approximate position is already known.

Diving procedure.

When the word "stand by to dive" is passed, the operator will perform the following operations:

Care of equipment during long dives.

To minimize troubles or possible damage, due to condensation and moisture, keep the canvas covers on all units; remove and dry these covers frequently if condensation is heavy. Also turn the power switch on (keep the transmitter plate high voltage switch off) for ten minutes every three hours. The controls in the transmitter unit and the receiver-indicator unit should not be touched.

PERFORMANCE

Maximum reliable range.

Minimum range.

The minimum range on aircraft is about 2,500 to 3,000 yards.

TROUBLES

Trouble is indicated in the SD radar by the following operational difficulties:

1. From 1/4 to 1 1/2 inches of grass are not present at all times when the sensitivity is turned to maximum.

3. Appearance of the transmitter flag does not remain substantially the same.

4. Internal interference is heavy and persistent.

5. Arcing is audible in the antenna during normal operation.

6. Bi-directional, or a non-uniform pattern of transmission is suspected.

7. Echoes and ranges on known land and friendly planes, appear to be below normal.