PART 4

SPECIFIC EQUIPMENT

ORDER OF PRESENTATION

SG RADAR
SC, SK RADARS
MARK 3, MARK 4 RADARS
SA RADAR
SL RADAR
SO RADAR
SF RADAR
SJ RADAR
SD RADAR


PART 4

SG RADAR

CONTROLS 4-SG-2
Range and train indicator 4-SG-2
Identification and function 4-SG-2
   
TURNING ON AND OFF 4-SG-4
Turning on 4-SG-4
Turning off 4-SG-4
   
CALIBRATION 4-SG-5
Calibration of the range counters 4-SG-5
External calibration 4-SG-6
   
OPERATIONAL TECHNIQUE 4-SG-6
Tuning the receiver 4-SG-6
  Land echo  
  Ship echo  
  Sea-return  
  Meter  
Long-range search or large target search 4-SG-7
Close-range search or small target search 4-SG-7
Station keeping 4-SG-8
Auxiliary fire control 4-SG-8
Navigation 4-SG-9
Composition 4-SG-9
  Type and number of ships  
  Aircraft  
  Land  
  False echoes  
  PPI echoes  
Jamming and deception 4-SG-11
   
PERFORMANCE 4-SG-12
Maximum reliable range 4-SG-12
Minimum range 4-SG-12
Accuracy 4-SG-12
Resolution 4-SG-12
TROUBLES 4-SG-12
 
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RADAR OPERATOR'S MANUAL
SG RADAR
CONTROLS

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.

  1. The switch marked A is the remote control for the main-power switch at the transmitter-receiver unit.

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

Drawing of the front of the range and train indicator unit.
Figure 4 SG-1. Range and train indicator unit.
 
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SG RADAR
unit. When switch K is an the RECEIVER TUNE position, it should read from 30 to 40 depending upon how well the receiver is tuned. The receiver should be tuned for maximum meter deflection. The meter reading in the MONITOR position will vary from time to time according to the way it is adjusted by the maintenance man. The operator should check the value at the start of his watch, and periodically thereafter, in order to determine whether any changes occur. The maintenance man should be notified immediately of any change.

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

  base on the range scope. Thus, lining up the step with the blip on the range scope, the range of the target can be read directly from the range counters.

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.

 
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RADAR OPERATOR'S MANUAL
22. 15,000-yard limit set (3) adjusts the calibration for the upper 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.

H center adjustment (12) centers the time base on the range scope from right to left.

V center adjustment (13) centers the up and down position of the time base on the scope.

PPI anode 2 (16) adjusts the sweep and signal intensity of the PPI screen.

PPI intensity (15) adjusts the intensity of the signal.

Marker amplitude (14) adjusts the height of the range markers, which should be from 3/4 inch to 1 inch in height.

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

  that he can make any adjustment automatically, even in complete darkness.

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:

1. Turn the main-line power at the remote control switch (A) to STANDBY.

2. Set the radiation switch (D) in the OFF position.

3. Turn the variac (E) to zero (extreme counterclockwise).

4. Place synchro switch (J) on NORMAL position.

5. Turn receiver gain (L) down.

6. Throw signal-markers switch (Q) to SIGNALS.

7. Turn bearing switch (R) to NORMAL.

8. Set rec-tune, normal, monitor switch (K) to NORMAL.

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:

1. Turn the standby-on switch (A) to the ON position. The amber pilot light will indicate that power is available. Check the line voltage on meter (B), which should read between 110 and 120 volts.

2. Throw the radiation switch (D) to LOCK position. After about one minute, the red pilot light will glow, indicating that the transmitter is ready.

3. Turn the variac (F) slowly to the right until the transmitter current meter reads 25 milliamperes or less.

4. Turn the receiver gain control (L) up until about 3/8-inch grass appears on the range scope.

5. Start antenna rotation by turning the switch (R) to right or left.

Turning off.

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

1. Stop antenna rotation by turning switch (R) to the center position, leaving antenna on 000 degrees relative bearing.
 
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SG RADAR
2. Turn receiver gain control (L) down.

3. Return variac (F) to zero (extreme counterclockwise).

4. Turn radiation switch OFF.

5. Throw the power switch (A) to STANDBY.

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

  appear along the time base on the range scope. The operator now turns the range crank (N) until the 15,000-yard marker just begins to "pull down" into the step. The diagram in figure 4 SG-2 illustrates how the step should appear when adjusted to the correct position. If accurate, the range counters should read exactly 15,000 yards. Next, the step is lined up with the center of the 5,000-yard marker. Now, the counter should read exactly 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

Under, over and correct calibration at 15,000- and 75,000-yard ranges scales.
Figure 4 SG-2. Correct calibration at 15,000- and 75,000-yard ranges scales.
 
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RADAR OPERATOR'S MANUAL
be visible at the left end of the time base. However, there should not be any confusion as to whether the first visible marker represents zero or 5,000 yards. If the zero marker appears, it will just he seen at the extreme left end of the time base. lithe first visible marker is some distance from the beginning of the time base, it is the 5,000-yard marker.

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:

1. Turn the signal-markers switch (Q) to MARKERS.

2. Set the range switch (P) to the 15,000-yard position.

3. Turn the range crank (N) until the range counter reads exactly 15,000 yards on the lower scale. Unlock the 15,000-yard limit set control (3), and adjust it until the top of the fourth range marker at the far right just begins to "pull down" into the step. Lock the control in this position.

4. Change the range switch (P) to the 75,000yard position. If the range crank has not been move], the top counter will read 75,000 yards. Unlock the 75,000-yard limit set control (5), and turn it until the 75,000-yard marker (fifteenth or sixteenth from the left) begins to "pull down" into the step. Then lock the control again.

5. Turn the range crank (N) until the top counter reads 5,000. Unlock the 75,000-yard zero set control (4), and adjust it until the 5,000-yard marker (first or second from the left) begins to drop. Lock the control.

6. Switch to the 15.000-yard range, and turn the range crank until the bottom counters read 5,000. Now unlock the 15,000-yard zero set control (2) and adjust it until the 5,000-yard marker begins to drop. Lock the control.

7. Re-check the upper limits on both range scales.

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

  by comparison with fire-control radar, by ranging on some target whose distance can he determined precisely, or by observation of a double range echo. A double range echo is a false echo that will sometimes appear on the same bearing as a target, but at twice the range of that target. These echoes are most evident when the target ship is on a parallel course, close abeam, and large. If the real echo appears at 800 yards and the double range echo appears at 1,800 yards, the correct range of the target will he the difference between the two, or 1,000 yards. Since, in this example, your radar measured the range as 800 yards, the set's individual, constant error would be 200 yards, making all ranges low by that amount.

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

 
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SG RADAR
then estimating the mean (average) setting between these two points. During tuning, always keep the signal below saturation by adjusting the receiver gain control (L), and make the setting rapidly.

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.

Sea Return Signal (Poor Timing) at the left A; (Some Signal in A After Adjusting Rec. Tuning Control) B
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

  search should use both the "A" and PPI scopes, with the following procedure:

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

 
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RADAR OPERATOR'S MANUAL
flat top drops off into the step. The illustration in figure 4 SG-4 shows the correct means of ranging on a saturated pip.

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

  may be estimated by simply rotating the scale to coincide with the target. This device has two disadvantages: first, the range scale is inaccurate; second, it obscures the view of the PPI. A more satisfactory device is under development.

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

Three illustrations of Over, Correct and Under Ranging.
Figure 4 SG-4 Correct method for ranging on a saturated signal on the 15,000-yard range scale.
 
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SG RADAR
possible to do very rough spotting in both range and deflection by estimation from the PPI.

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

  hounded by coral reefs and shoals, so extreme caution must be observed while using radar navigational fix taken close to them. Lack of small prominent points on these islands makes it difficult to obtain reliable fixes.

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.

 
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Multiple-reflection echoes are caused by the beam reflecting between several ships in a group before returning to the antenna. The bearing of the echo will be the same as one of the ships. Because of the changing position of the ships, this type of echo will disappear very quickly.

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

  81 miles away. Trouble will be experienced with this type of echo only when there is high land over 81 miles away. In order to know when second-sweep echoes are likely to be encountered, the operator should be constantly aware of the ship's position in relation to land. To check this type of false echo, the pulse rate should be changed. If the echo is of the second-sweep type, it will shift in range or disappear entirely. Although these echoes are rare, they should be recognized and understood. Figure 4 SG-5 shows a graphic representation of how the second-sweep echo pip will shift its position on the "A" scope as the pulse frequency is varied.

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

Second-sweep echoes.
Figure 4 SG-5. Second-sweep echoes.
 
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interfering structure. The SG also has side lobes 60 degrees to 70 degrees on either side of the main lobe. They will often show up on a large target which is within 5,000 yards.

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:

1. DF on the jamming.

2. Use available anti-jamming devices on receiver when provided.

3. Try moving the gain control up and down.

4. Try changing the receiver local oscillator tuning.

5. Keep operating.

6. Report the type and bearing of jamming to CIC.

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

  always be on some certain relative bearing regardless of own-ships course changes.

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:

1. Reduce setting; this prevents overload of radar receiver; echoes are visible "riding on top" of the jamming pattern.

2. Increase setting; this limits (or clips) jamming; echoes are visible as a break in the base line.

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


* See Part 3, Defense Against Jamming and Deception.
 
4-SG-11

RADAR OPERATOR'S MANUAL
in some cases, this information should he reported if possible. If the equipment is provided with an anti-jamming receiver, the jamming may be reduced sufficiently for reading targets without any detuning of the receiver. Detuning should be undertaken as a last resort, and then should be done very carefully and cautiously; otherwise all targets may be lost and the procedure made completely ineffective. No special method is offered for setting the controls of the AJ receiver, except that they should be varied for minimum jamming, the gain control coming first, and then the A\TC control.

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.

  Accuracy.

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,

Type of target. SG SG-A and SG-1
BB, CV, Large auxiliaries 35,000-45,000 yards 45,000-55,000 yards
CA, CL, Medium auxiliaries 28,000-35,000 yards 30,000-40,000 yards
DD, DM, AV, PC 18,000-30,000 yards 25,000-35,000 yards
Submarines 9,000-12,000 yards 11,000-15,000 yards
Submarine periscope 2,000-4,000 yards 2,000- 4,000 yards
Large planes (altitude 1000'-3000')
PBM, PBY, PBZ
20,000-35,000 yards 20,000-40,000 yards
Small planes (altitude 1000'-3000')
SOC, OSZU, SBD, F4F
10,000-15,000 yards 12,000-21,000 yards
 
Minimum range. SG SG-A and SG-1
Ship 600 yards 600 yards
Plane 1,000 yards 1,200 yards
 
4-SG-12

SG RADAR
If the antenna and "bug" will not turn when the antenna is switched to automatic rotation, the bearing 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

  as a series of markers described through 360 degrees. When this condition exists, the operator should do the following:

1. Shift the switch on the gyro-control panel from the forward gyro to the after gyro supply or vice versa.

2. If this does not correct the situation, shift the synchro switch on the R and T indicator from NORMAL to EMERGENCY and continue to operate, reading relative bearing only on the outer dial.

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.

 
4-SG-13

PART 4

SC-SK RADAR

CONTROLS 4-SC/SK-2
Control unit 4-SC/SK-2
Receiver unit 4-SC/SK-3
Indicator unit 4-SC/SK-3
PPI unit 4-SC/SK-4
Preamplifier Unit 4-SC/SK-4
   
TURNING ON AND OFF 4-SC/SK-4
Turning on 4-SC/SK-4
Turning off 4-SC/SK-4
   
CALIBRATION 4-SC/SK-4
Calibrating the range scope 4-SC/SK-4
Calibrating the PPI 4-SC/SK-4
Modification of PPI scope 4-SC/SK-6
   
OPERATIONAL TECHNIQUE 4-SC/SK-6
Tuning the receiver 4-SC/SK-6
Long-range search 4-SC/SK-6
Searching over land 4-SC/SK-6
Multiple-target tracking 4-SC/SK-7
Fighter-director tracking 4-SC/SK-7
Fire-control liaison 4-SC/SK-7
Composition 4-SC/SK-7
Jamming and deception 4-SC/SK-8
   
PERFORMANCE 4-SC/SK-9
Maximum reliable range 4-SC/SK-9
Minimum range 4-SC/SK-9
Accuracy 4-SC/SK-9
Resolution 4-SC/SK-9
   
TROUBLES 4-SC/SK-10
 
4-SC/SK-1

RADAR OPERATOR'S MANUAL
SC-SK RADAR
The SC radar is now obsolete and will not be dealt with in this discussion. The controls on the control unit and the receiver indicator unit, which the operator uses, are the same as those of the SC-1. The SC-1 radar is a modification of the SC. The transmitter was re-designed to increase the power output, and the antenna was modified. A preamplifier unit has been added to most sets.

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:

1. The control unit.
2. The receiver indicator unit.
3. The transmitter.
4. The preamplifier.
5. The plan position Indicator unit.
 
6. The antenna, together with transmission line and duplexer units.

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.

Figure 4 SC/SK-1. Receiver, indicator and control unit.
Drawing of receiver, indicator and control unit front panel.
 
4-SC/SK-2

SC-SK RADAR
D. Remote bearing indicator switch: applies control power to remote bearing repeaters.

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.

  DD. Dial light brightness control: controls brightness of the pilot lights and range-counter lights on the indicator unit.

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:

Range 1-30,000 yards
Range 2-75 miles
Range 3-375 miles
Drawing of the plan position indicator and its switches.
Figure 4 SC/SK-2. Plan position indicator.
 
4-SC/SK-3

RADAR OPERATOR'S MANUAL
VV. Remote range mark: remote alarm 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:

Range 1-20 miles
Range 2-75 miles
Range 3-200 miles

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.

  3. Turn ON receiver indicator power switch (ZZ). Pilot light (RR) and the lights on the range counter will light. After a few seconds, a trace will be seen on the range scope, unless the brilliance control (EE) is fully counterclockwise.

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

 
4-SC/SK-4

SC-SK RADAR
calibration so that a stationary figure of eight is observed. Lock control. (See fig. 4 SC/SK-3.)

6. Turn crystal switch (PP) to OFF.

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

Figure of eight determines when calibration pips are 2,000 yards apart.
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.

  13. Turn (CC) to RECEIVE. This method of calibration differs from that given in the instructional manual.
We use this method for three reasons:

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.

Pattern for calibrating minimum range on range 1.
Figure 4 SC/SK-4. Pattern for calibrating minimum range on range 1.
 
4-SC/SK-5

RADAR OPERATOR'S MANUAL
Modification of PPI scope.

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.

1. Make a center for the drafting compass out of a small piece of plastiglass in which you have drilled a shallow hole to hold the compass point.

2. Secure this center to the center of the PPI scope with scotch tape.

3. Using the radii of the range circles on the filter, ink solid circles on the scope face. To facilitate direct reading of the 75-mile range scale, ink in two dashed circles evenly spaced between the solid circles.

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

  all, or when there are one or more target indications on the screen which have been identified and are of interest to the CIC watch officer only, as to their general position. The CIC officer will get most of the information he desires from his repeater scope, but a rough plot should also he kept. Readings every three minutes are usually sufficient for this plot.

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:

1. PPI scope on 200-mile range scale, and "A" scope on 75-mile range scale, or

2. PPI scope on 75-mile range scale, and "A" scope on 375-mile range scale.

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

 
4-SC/SK-6

SC-SK RADAR
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 to get them.

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,

  the PPI should be operated on the 20-mile range. The gain should he reduced to an amount just sufficient to keep the targets at the longest ranges appearing on the scope. This will eliminate some side lobes and reduce strength on all side lobes while holding echoes from the main lobe on the screen. This method of operation eliminates any chance of observing planes coming in at ranges greater than 20 miles, but is the most effective method when the primary purpose is fire-control coaching. At GQ, the standby operator can keep the fighter director officer informed of the general situation outside 20 miles by observing the range scope and taking ranges and bearings with continuous antenna rotation.

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

 
4-SC/SK-7

RADAR OPERATOR'S MANUAL
move slowly with occasional fading out, are characteristic of these targets, although sharp narrow pips have been observed. If identification is difficult by looking at the pip, a plot should be made to determine the course and speed. This should then be compared with the course and speed of the wind, which is the best check outside of actual observation.

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:

1. DF on the jamming.
2. Use available anti-jamming devices on the receiver when provided.
3. Try moving the gain control up and down.
4. Try changing the receiver local oscillator tuning.
5. Keep operating.
6. Report the type and bearing of jamming to CIC.

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

  accidental interference instead. Jamming will not only be directional, but its true hearing will not he 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 always be on some certain relative bearing regardless of changes in own ship's course.

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:

a. Reduce setting; this prevents overload of the radar receiver; echoes are visible "riding on top" of the jamming pattern.

b. Increase setting; this limits (or clips) jamming; echoes are visible as a break in the base line.

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

 
4-SC/SK-8

SC-SK RADAR
time to time, and 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 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.


* See Part 3, Defense Against Jamming and Deception.
  Maximum reliable range.

SC-2 RADAR

Antenna 90 feet

BB, CV, CB, Large auxiliaries 37,800 yards
CA, CL, Medium auxiliaries 25,000 yards
DD, DE, DM, AV, PC, CG 17,000 yards
Submarines 5,900 yards
Large planes, PBM, PB2Y 132,000 yards
Small planes, 6F6, TBF, SB2C 72,500 yards
Land 142 miles

SK RADAR

Antenna 130 feet

BB, CV, CB, Large auxiliaries 51,500 yards
CA, CL, Medium auxiliaries 35,000 yards
DD, DE, DM, AV, PC 226,500 yards
Large planes 250,000 yards
Small planes 150,000 yards
Land 170 miles

Minimum range.

SC-1, SC-2, SK "A" scope 1,500 yards
PPI
20-mile range 2 1/2 miles
75-mile range 6 miles

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.

Ranges Sweeping Stopped
  Range Bearing Range Bearing
30,000 yards 1,000 3 degrees 200 5 degrees
20 miles 1/2 mile 3 degrees   5 degrees
75 miles 1 mile 3 degrees 1 1/2 mile 5 degrees
200 miles 2 miles 3 degrees   5 degrees
375 miles 5 miles 3 degrees 1 mile 5 degrees

Resolution.

Bearing 10 degrees
Range 500 yards
 
4-SC-SK/9

RADAR OPERATOR'S MANUAL
TROUBLES

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

  turn the high voltage variac back to its normal operating position. Should the relay continue to kick out, notify the maintenance man as to what occurred and what has been done.

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.

 
4-SC/SK-10

PART 4

MARK 3 AND MARK 4 RADAR
(FC, FD)

CONTROLS 4-Mk. 3/Mk. 4-2
Main unit 4-Mk. 3/Mk. 4-2
Control and indicator unit (range scope) 4-Mk. 3/Mk. 4-2
Range unit 4-Mk. 3/Mk. 4-3
Train or elevation indicator 4-Mk. 3/Mk. 4-3
 
TURNING ON AND OFF 4-Mk. 3/Mk. 4-4
Turning on the main unit 4-Mk. 3 Mk. 4-4
Turning off the main unit 4-Mk. 3 Mk. 4-4
Turning on the control and indicator (C&I) unit 4-Mk. 3/Mk. 4-4
Turning off the control and indicator unit 4-Mk. 3/Mk. 4-5
Turning on the trainers and pointer's scopes 4-Mk. 3/Mk. 4-5
Turning off the trainer's and pointer's scopes 4-Mk. 3/Mk. 4-5
Tuning the receiver 4-Mk. 3/Mk. 4-5
 
CALIBRATION 4-Mk. 3/Mk. 4-6
Range zero set 4-Mk. 3/Mk. 4-6
Double range echo method of obtaining zero set 4-Mk. 3/Mk. 4-7
Train and elevation calibration 4-Mk. 3/Mk. 4-7
 
OPERATIONAL TECHNIQUE 4-Mk. 3/Mk. 4-8
The range operator 4-Mk. 3/Mk. 4-8
The trainer and the pointer 4-Mk. 3/Mk. 4-8
Searching with bearings and ranges given 4-Mk. 3/Mk. 4-9
Searching when no bearings or ranges are given by the search radar 4-Mk. 3/Mk. 4-9
Tracking 4-Mk. 3/Mk. 4-9
Spotting 4-Mk. 3/Mk. 4-10
Determining composition 4-Mk. 3/Mk. 4-11
Anti-jamming technique 4-Mk. 3/Mk. 4-11
 
PERFORMANCE 4-Mk. 3/Mk. 4-13
Maximum reliable ranges 4-Mk. 3/Mk. 4-13
Minimum ranges 4-Mk. 3/Mk. 4-13
Accuracy characteristics 4-Mk. 3/Mk. 4-13
Resolution 4-Mk. 3/Mk. 4-13
 
TROUBLES 4-Mk. 3/Mk. 4-14
 
4-Mk. 3/Mk. 4-1

RADAR OPERATOR'S MANUAL

MARK 3 AND MARK 4 RADAR
(FC, FD)

CONTROLS

Main unit.

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

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

Line drawing of the main unit.
Figure 4 Mk. 3/Mk. 4-1. Main unit.

  3. Load voltage: should be set to 120 at all times by means of control No. 11. (A recent directive says 115, but do not set it at 115 unless the set has been adjusted for this.)

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.

 
4-Mk. 3/Mt. 4-2

MARK 3 AND MARK 4 RADAR
6. Lobing on-off switch: turns lobing motor on or off.

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.

Line drawing of control and indicator unit.
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.

  Line drawing of range unit.
Figure 4 Mk. 3/Mk. 4-3. Range unit.

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

 
4-Mk. 3/Mk. 4-3

RADAR OPERATOR'S MANUAL
4. Focus control: focuses the image.

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.

  If not, adjust to this value by magnetron filament voltage adjustment (21).

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.

Every time the main unit is turned on from a cold start, the wear on the set is equivalent to three hours steady running of the set. Thus, if the set is to be turned off and on eight times a day it would be more profitable to let the set run continuously.

Another even more important consideration in this respect is that it requires approximately three hours running before the set is warmed up sufficiently for most accurate operation. If the modulation generator has a red light at the top of the front panel which flashes off and on, it will take a much shorter time to warm up (approximately one hour).

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.

 
4-Mk. 3/Mk. 4-4

MARK 3 AND MARK 4 RADAR
5. Turn the receiver sensitivity control (3) clockwise until the grass is about a half-inch high.

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

  connected to the grounded side which on RCA scopes is marked with a zero. The RED, or high side is connected to the top of the two vertical terminals which are marked high. Plug this cord into the right hand plug of the four jacks in the radar receiver panel; this is marked mon (18).

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

 
4-MR. 3/Mk. 4-5

RADAR OPERATOR'S MANUAL
lock in and cease to move, The image thus formed will be the same picture that is on the C and I scope in the director, except there will be no notch and there will be no expanded portion of the sweep. It should be noted here, that the operator might find the actual tuning procedure, which is about to be described, easier if he stops the image on the screen with two pips on it rather than one. This is largely a matter of preference, By adjusting the horizontal gain and the horizontal centering knobs, the operator can make the two pips line up with the divisions on the graduated face of the scope. By counting the number of divisions between the pips, and realizing that this distance corresponds to 100,000 yards, it is possible for him to estimate roughly the distance to any target.

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.)

  3. Loosen the inner knurled nut (1) located above the range crank,

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.

Transmitter pulse position for correct zero set.
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.

 
4-Mk. 3/Mk. 4-6

MARK 3 AND MARK 4 RADAR
Double range echo method of obtaining zero set.

(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.)

Double range echo.
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

  distance between the first and second echoes, namely 1,500 yards.

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


* Note: This is a technician or Navy Yard job.
 
4-Mk. 3/Mk. 4-7

RADAR OPERATOR'S MANUAL
stay on a small, distant target with their optics. The maintenance man watches the pips on the trainer's scope, and directs the men adjusting the antenna to move it to the right or left, as indicated by the pips on the trainer's scope. When the pips are even, the antenna is locked in place.

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

  range operator will find that after once setting up the scope correctly, there are only two knobs that require further adjusting. but those two knobs will have to be adjusted frequently. These are the image spread (2) control, and the receiver sensitivity (3) control. The receiver sensitivity must be readjusted as often as necessary, to prevent saturation of the pips seen on the pointer's and trainer's scopes. He should make all adjustments on the range scope with his left hand (or with his right if his left hand is on the range knob). He must know the position of all controls so well that he can make adjustments to the scope without groping for the knob or taking his eyes from the scope.

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

 
4-Mk. 3/Mk. 4-8

MARK 3 AND MARK 4 RADAR
When the pips are of the same height, the pointer and the trainer say. mark," or "on train," or "on point." Occasionally you will notice that the pips will act in reverse, in other words, when you train or point toward the lower pip, it will get lower rather than higher. This indicates that you have a minor lobe contact. The target actually bears 15 degrees to 20 degrees to the left or right of this.

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

  in the notch. To help speed op the process of getting the pip in the notch, the operator should have previously cranked onto his range dial the range given by the search gear. If the target should disappear, close the notch, hold the train and elevation and turn the range knob back and forth. Soon the pip will show up again, and this time the operator will be able to get it into the notch; the pointer and the trainer will also get a fix or an indication of which way to train or elevate before it disappears. This process should be continued patiently. If the pip is clear the range operator knows that the pointer and or trainer are on target. If the pip is cloudy, the trainer and pointer are off the target. On some targets, however, such as a flight of planes, it will be impossible to get a clear pip.

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

 
4-Mk. 3/Mk. 4-9

RADAR OPERATOR'S MANUAL
we are simply waving the same beam back and forth in front of the director. It is easier to spot a target quickly with the increased beam width than it would be if you had only the one 9 degree beam.

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 computer 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

  the target, thus not transmitting ranges continuously. Accordingly, a set-up on the director can be made more quickly by using radar ranges and rate control on the director than by any other means.

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

 
4-Mk. 3/Mk. 4-10

MARK 3 AND MARK 4 RADAR
width of the notch. Some ships have installed a scotch tape scale on the face of the range scope to aid in spotting.

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

  classified as unintentional interference rather than jamming.

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

 
4-Mk. 3/Mk. 4-11

RADAR OPERATOR'S MANUAL
the transmitter slightly by varying the field control, and the plate voltage of the magnetron, or by varying the duplexer tuning. This method is valuable, but the jammer may shift to your new frequency. Changing the receiver local oscillator tuning at the main frame may also be of some assistance.

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.

  The official policy is to keep your transmitter on at all times, attempting to work through the jammer, even though at first glance it may seem impossible to do so. Perseverance and patience will be rewarded many times by your being able to range on the target. Because the echoes increase more rapidly with decreasing range than the jamming signal increases, it may he possible to suddenly see the pip from a closing target. This is another reason for leaving the transmitter on at all times.

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 3 RADAR
  75' Antenna height 125' Antenna height
Type Without preamp. With preamp. Without preamp. With preamp.
Large ships-(BB, CV, Large Aux.) 17,500 20,000 20,500 27,000
Medium ships-(CA, CL, Med. Aux.) 15,000 17,000 18,500 25,500
Small ships-(DD, DM, AD, PC, etc.) 11,500 13,000 13,500 18,000
Submarine (surfaced) 4,500 -- 10,000 7,000
Submarine (periscope) 2,500 -- -- --
Large planes-(PBM, PBY, PB2Y, etc.) 25,500 20,500 23,000 36,500
Small planes-(SOC, OS2U, SBD, F4F, etc.) 14,000 8,000 15,000 --

RELIABLE RANGES OF MARK 4 RADAR

  75' Antenna height 125' Antenna height
Type Without preamp. With preamp. Without preamp. With preamp.
Type Without preamp. With preamp. Without preamp. With preamp.
Large ships 16,000 18,500 15,500 26,000
Medium ships 12,000 15,500 16,000 25,000
Small ships 9,000 11,000 11,000 18,000
Submarine (surfaced) 3,500 -- 7,000 --
Submarine (periscope) -- -- 4,000 --
Large planes 22,500 16,000 21,000 47,000
Small planes 13,500 13,500 13,000 23,500
 
4-Mk. 3/Mk. 4-12

MARK 3 AND MARK 4 RADAR
PERFORMANCE

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

  not perpendicular to the shore line, the bearing resolution of the set comes into the problem, and it will be more difficult to pick up the target. The greater the deviation from the perpendicular, the farther out from the beach the target will have to be to be distinguished from the land by the radar. This can be seen in figure 4 Mk. 3/Mk. 4-8.

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.

Characteristic FC long ant.
(3' X 12')
FC Short ant.
(6' X 6')
FC Antenna
(6' X 7')
Maximum range by direct indication (nominal range) 100,000 yds. 100,000 yds. 100,000 yds.
Minimum range (approx.) 1,000 yds. 1,000 yds. 1,000 yds.
Horizontal beam width (lobing off) 4.6 degrees 9.0 degrees 9.0 degrees
Vertical beam width (lobing off) 30.0 degrees 11.0 degrees 19.0 degrees
Horizontal beam width (lobing on) 7.2 degrees 15.0 degrees 15.0 degrees
Vertical beam width (lobing on) 30.0 degrees 11.0 degrees 15.0 degrees
Range accuracy +/-40 yds. +/-40 yds. +/-40 yds.
Bearing accuracy +/-2 mils +/-4 mils +/-4 mils
Elevation accuracy* -- -- +/-4 mils
Range resolution +/-400 yds. +/-400 yds. +/-400 yds.
Bearing resolution +/-5 degrees +/-10 degrees +/-10 degrees
Elevation resolution* -- -- +/-10 degrees
* Elevation data applies only when antenna is elevated above 10 degrees.
 
4-Mk. 3/Mk. 4-13

RADAR OPERATOR'S MANUAL
What has previously been said regarding the horizontal plane, also applies to the vertical plane. The elevation resolution is 10 degrees.

Target can be ranged on, since it is off shore a distance in excess of the range resolution of the Mk.3 and Mk.4; Land at same range obscures target; Target clear of land echo, and can be ranged upon. The spread of land due to beam width distortion is shown.
Figure 4 Mk. 3/Mk. 4-8.

 
TROUBLES

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.

 
4-Mk. 3/Mk. 4-14

PART 4

SA RADAR
CONTROLS 4-SA-2
Power control 4-SA-2
Selection switches 4-SA-3
Operating controls and indicators 4-SA-4
Adjustments 4-SA-4
Alarms 4-SA-5
 
TURNING ON AND OFF 4-SA-5
Turning on 4-SA-5
Turning off 4-SA-5
 
CALIBRATION 4-SA-5
 
OPERATIONAL TECHNIQUE 4-SA-6
Tuning the receiver 4-SA-6
Miscellaneous adjustments 4-SA-6
Long-range search 4-SA-6
Searching over land 4-SA-7
Reading hearings on the fly 4-SA-7
Tracking 4-SA-7
Fire-control liaison 4-SA-8
Jamming and deception 4-SA-8
 
PERFORMANCE 4-SA-9
Maximum reliable range 4-SA-9
Minimum range 4-SA-10
Range accuracy 4-SA-10
Bearing accuracy 4-SA-10
 
TROUBLES 4-SA-10
 
4-SA-1

RADAR OPERATOR'S MANUAL

SA RADAR

CONTROLS

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

  indicator circuits. When it opens, no trace appears on the screen and no dial lights come on.

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.

Drawing of transmitter unit.
Figure 4 SA-1. Transmitter unit.

 
4-SA-2

SA RADAR
P-12. Fil. voltage meter (on transmitter): indicates voltage on the primary of the filament transformer that supplies voltage to the filaments of the oscillator tubes. Control P-11, should be adjusted until the meter reads the same voltage as that marked on the small card above it.

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

  depend on the TCA for power. If the TCA should fail, this switch permits a continuation of the search.

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

Figure 4 SA-2. Receiver indicator unit.
Figure 4 SA-2. Receiver indicator unit.
 
4-SA-3

RADAR OPERATOR'S MANUAL
the screen, and on the "osc. adj. scope" (2-inch CRT). When in position 1, any strong signal occurring at a rate of about 60 cycles per second will "synchronize the sweep" so that a strong pulse will appear fairly steady on the sweep. This is called internal synchronization. In position 2, the sweep on the scope is started by the transmitter pulse.

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

  white bug used when lobe switching and matching pips.

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.

 
4-SA-4

SA RADAR
Ad-12. First R.F.: receiver tuning adjustment.

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.

a. Transmitter power OFF.
b. Slewing motor OFF.
c. L-R motor OFF.
d. Emergency train-AUTO.
e. Antenna train-TRUE (if ship's gyro compass is operating properly).
f. Plate voltage control fully counterclockwise.
g. Receiver gain down (fully CCW).
h. Intensity down (fully CCW).

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.

  3. Alter about 30 seconds, a relay will snap in the TCA.

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

 
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RADAR OPERATOR'S MANUAL
yards; next adjust cal-min so the step is accurately aligned with the beginning of the second range mark. This adjustment is correct when the little peak just beyond the right-hand end of the first range mark is leveled up with the end of that mark (at the beginning of the second range mark). (see fig. 4 SA-3.)

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.

Display showing 6 peaks.
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

  vertical control until the trace appears directly above the scale.)

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

 
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attention to the left-hand portion of the time base. Again readjust gain, astigmatism, and intensity controls slightly, if necessary. Repeat in order, the steps outlined above.

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

  the bug. For each individual, this time is practically constant; in other words, the bearing error will be practically constant. When an operator determines the magnitude of his individual "error" he can read the bug, correct for his "error" and report the corrected reading. An example will serve to make this clear.

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

 
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RADAR OPERATOR'S MANUAL
scale marked on the front of the scope. (Do not use the range step.) If the plane is close on initial contact, you can save valuable time by reporting it as a bogey without interrogating first. The next time around, interrogate, estimate composition, get accurate bearing and range, and see whether they are opening or closing range, or crossing. Report. Snap cal-fide-IFF switch to position 4 to check for IFF-response.

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.

  Also the antenna must be kept bearing on the target. The operator does this by keeping the two pips from the target matched in height; it may be necessary to reduce the gain to keep these pips below saturation. He keeps the two steps lined up with the two pips, and reads the ranges indicated on the counters.

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:

1. DF on the jamming.
2. Use available anti-jamming devices on receiver when provided.
3. Try moving gain control up and down.
4. Try changing receiver local oscillator toning.
5. Keep operating.
6. Report type and bearing of jamming to CIC.

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

 
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directional, but its true bearing will not be changed by any sudden change in your ships course. Interference originating aboard your own ship will either be non-directional and appear on all bearings, or else it will always be on some certain relative bearing regardless of your own ships course changes.

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:

a. Reduce setting; this prevents overload of the radar receiver; echoes are visible "riding on top" of the jamming pattern.

b. Increase setting; this limits (or clips) jamming; echoes are visible as a break in the base line.

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

  change from time to time, so if you are persistent enough some information may be obtainable.

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

BB, CV. CB, Large auxiliary 43,900 yards
CA, CL, Medium auxiliary 24,900 yards
DD, DM, AU, PC, CG, etc 15,600 yards
Submarines (surfaced) 4,500 yards
Large planes-PBM, PB2Y, PBY 40 miles
Small planes-SOC, SBD, F6F 20 miles
Groups of planes 60-80 miles
Land (1,500 feet or higher) depending on atmospheric condition 90-200 miles
Low flying planes 10-15 miles

* See Part 3, Defense Against Jamming and Deception.
 
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RADAR OPERATOR'S MANUAL
Minimum range.
Ships-depends on sea-return 750-2,000
Planes 1.0 mile

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