Exercise 3-1 Deceptive Jamming Using Amplitude-Modulated ... · Deceptive Jamming Using Amplitude-Modulated Signals 3-9 During the third part of the exercise, you will observe and

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Exercise 3-1

Deceptive Jamming Using Amplitude-Modulated Signals

EXERCISE OBJECTIVE

To demonstrate the effect of AM noise and repeater inverse gain jamming, twoangular deceptive EA used against sequential lobing radars. To outline the reasonswhy radar PRF agility is an effective EP against inverse gain jammers.

DISCUSSION

Introduction

As stated in this Unit's Discussion of Fundamentals, conical scan and sequentiallobing radars, unlike monopulse radars, are vulnerable to amplitude-modulatedjamming signals. These radars operate by moving their antenna beam to induce anamplitude modulation onto the target echo signal for the purpose of angular tracking.When the radar antenna is pointed directly toward the tracked target, the amplitudeof the target echo signal is constant over time. Non-radar induced amplitudevariations onto the target echo signal, due to scintillation or a jamming signal, are acause of error and uncertainty in the target’s angular position as seen by the radar.

Inverse Gain Jamming

Inverse gain jamming, an angular DECM, consists in directing either a false targetsignal (repeater inverse gain jamming) or a noise jamming signal (AM noisejamming) toward the radar antenna with an amplitude modulation in phaseopposition to that generated by the scanning (or lobing) radar beam.

The transmitted amplitude modulation can be implemented either as a direct inverseof the radar’s amplitude modulation, or as on-off modulation, whereby the "on" periodis made to coincide with the interval when the radar-signal amplitude is minimum.Either of these types of amplitude modulation can cause an apparent angular errorin the radar’s tracking system. This apparent tracking error is opposite in sign to theactual tracking error needed to correct for the radar antenna’s angular position, asis illustrated in Figure 3-2 (a). In this figure, erroneous angular tracking informationis introduced into the radar angle tracking loop, because the amplitude of the targetecho signal, received through one lobe, has been made greater by the presence ofthe jamming signal.


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Figure 3-2. Inverse gain jamming against a sequential lobing radar.


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Synchronicity

For inverse gain jamming to be effective, the frequency at which the jamming signalis amplitude modulated must be near the victim radar’s lobing (or scan) rate. Inversegain jamming is effective when the jamming signal is synchronized with the radarantenna’s lobing (or scan) rate. However, it can also be effective in an asynchronous(sweeping) mode which searches for the most suitable amplitude modulationfrequency that perturbs the radar angle tracking loop. Figure 3-2 (a) shows repeaterinverse gain jamming synchronized to the radar lobing rate. Figure 3-2 (b) shows AMnoise jamming transmitted asynchronously to the radar lobing rate.

When transmitted synchronously, the jammer’s amplitude modulation frequency isset equal to the radar's lobing (or scan) rate. This introduces a fixed angular errorinto the radar’s angle tracking loop, resulting in an angular offset that deviates theradar antenna axis from the tracked target’s direction.

When transmitted asynchronously, the amplitude modulation frequency of thejamming signal may be slightly higher or lower than the radar's lobing (or scan) rate.This effectively creates a radar angular error signal with a beat frequency. The beatfrequency is equal to the difference between the amplitude modulation frequency ofthe jamming signal and that induced onto the target echo signal by the radar (i.e., theradar lobing or scan rate). The jammer must set its amplitude modulation frequencycarefully so that the beat frequency is low enough to pass through the angularservomechanism’s bandwidth (typically in the range of a few Hertz). Otherwise, theeffect of the received jamming signal is greatly attenuated by the angular trackingloop and, consequently, angular tracking is affected barely, or not at all.

Inverse Gain Jamming with the Lab-Volt Radar Jamming Pod Trainer

The Radar Jamming Pod Trainer, as stated in Exercise 2-1, can on-off modulateeither the repeater signal, or the noise jamming signal. Therefore, the RadarJamming Pod Trainer can produce either repeater asynchronous inverse gainjamming, or asynchronous AM noise jamming. The on-off amplitude modulationfrequency for these techniques can be set close to the tracking radar's lobing rate.The modulation frequency is changed using the Radar Jamming Pod Trainer remotecontroller.

Radar Electronic Protection Against Inverse Gain Jamming

Asynchronous and synchronous inverse gain jamming can be rendered ineffectiveagainst a conical scan or sequential lobing tracking radar by randomly changing, ona pulse-to-pulse basis, the radar’s pulse repetition frequency (PRF). Radars thathave this ability are said to have PRF agile emitters. PRF agility is a useful radarelectronic protection to inverse gain jamming. Patterned radar emitters, such asthose that can enable a staggered PRF, are only effective in reducing the amplitudeof the angular error caused by inverse gain jammers. They cannot eliminate theangular error completely. To completely eliminate the angular error, a PRF agileemitter is required. Unfortunately, truly PRF-agile radar emitters pose many designchallenges when implemented in pulsed Doppler radars. These radars require theirPRF to remain constant during their coherent processing interval (at least severalconsecutive pulse periods long).


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Silent lobing, also known as COSRO or LORO, and as briefly discussed in this Unit'sDiscussion of Fundamentals, is a radar EP designed to counter EA using amplitude-modulated jamming signals. However, silent lobing is not a 100% effectivecountermeasure to inverse gain jamming. The reason is, that a potentialasynchronous inverse gain jammer could slowly scan through the range of possiblepulse repetition frequencies and locate the value of the actual radar PRF. This isdone by observing which amplitude modulation frequency causes the greatestangular tracking error for the radar.

Certain conical scan and sequential lobing radars use an additional receive-beamthat is scanned or lobed (depending on the radar) at the same rate as the mainbeam. However, the additional receive-beam is displaced in angle by half arevolution (180°) with respect to the main beam (it is pointed in a direction about theantenna's axis that is opposite to that of the main beam in the case of sequentiallobing radars), as is illustrated in Figure 3-3. The outputs from the main beam andadditional receive-beam are used to create the radar’s angular tracking error signal.This technique, known as scan-with-compensation, is an effective EP that reducesthe amplitude modulation of the target echo signal produced using amplitude-modulated jamming signals.

Figure 3-3. A secondary receive-antenna beam is used in the scan-with-compensation technique.

Procedure Summary

During the first part of this exercise, you will set up and calibrate the Tracking Radar.You will also position the Target Positioning System with respect to the TrackingRadar.

In exercise part two, the equipment setup for demonstrating asynchronous inversegain jamming is made. The Radar Jamming Pod Trainer is positioned on the targetpositioning table. A metal plate target is added to the Radar Jamming Pod Trainerso as to provide it with a natural radar echo. The effect which inverse gain jamminghas on the radar video signal is observed on the Oscilloscope.


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During the third part of the exercise, you will observe and list the effects that anamplitude modulated noise jamming signal (AM noise jamming) has on the radar’sangular tracking. You will verify whether staggered PRF and PRF agility areappropriate radar EP to AM noise jamming, which is a form of asynchronous inversegain jamming.

During the final part of the exercise, you will demonstrate asynchronous inverse gainjamming using the Repeater of the Radar Jamming Pod Trainer. You will verify theefficiency of staggered PRF and PRF agility as radar EP against this form ofasynchronous inverse gain jamming.

PROCEDURE

Setting Up the Tracking Radar

G 1. Before beginning this exercise, the main elements of the Tracking RadarTraining System (i.e., the antenna and its pedestal, the target table, theRTM and its power supply, the training modules, and the host computer)must be set up as shown in Appendix A.

On the Radar Transmitter, make sure that the RF POWER switch is set tothe STANDBY position.

On the Antenna Controller, make sure that the MANual ANTENNAROTATION MODE push button is depressed and the SPEED control is setto the 0 position.

Turn on all modules and make sure the POWER ON LED's are lit.

G 2. Turn on the host computer, start the LVRTS software, select TrackingRadar, and click OK. This begins a new session with all settings set to theirdefault values and with all faults deactivated. If the software is alreadyrunning, click Exit in the File menu and then restart the LVRTS software tobegin a new session.

G 3. Connect the modules as shown on the Tracking Radar tab of the LVRTSsoftware. For details of connections to the Reconfigurable Training Module,refer to the RTM Connections tab of the software.

Note: Make the connections to the Analog/Digital OutputInterface (plug-in module 9632) only if you wish to connect aconventional radar PPI display to the system or obtain anO-scope display on a conventional oscilloscope.

Note: The SYNC. TRIGGER INPUT of the Dual-Channel Samplerand the PULSE GENERATOR TRIGGER INPUT of the RadarTransmitter must be connected directly to OUTPUT B of theRadar Synchronizer without passing through BNC T-connectors.

Connect the hand control to a USB port of the host computer.


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G 4. Make the following settings:

On the Radar Transmitter

RF OSCILLATOR FREQUENCY . . . . . . . CAL.PULSE GENERATOR PULSE WIDTH . . . 1 ns

On the Radar Synchronizer / Antenna Controller

PRF . . . . . . . . . . . . . . . . . . . . . . . . . . . 288 HzPRF MODE . . . . . . . . . . . . . . . . . . . . . SINGLEANTENNA ROTATION MODE . . . . PRF LOCK.DISPLAY MODE . . . . . . . . . . . . . . . POSITION

On the Dual-Channel Sampler

RANGE SPAN . . . . . . . . . . . . . . . . . . . . . 3.6 m

In the LVRTS software

System Settings:Log./Lin. Mode . . . . . . . . . . . . . . . . . . . . Lin.Gain . . . . . . . . . . . . . . . . . . . . . . as required

Radar Display Settings:Range . . . . . . . . . . . . . . . . . . . . . . . . . 3.6 m

G 5. Connect the cable of the target table to the connector located on the rearpanel of the Target Controller. Make sure that the surface of the target tableis free of any objects and then set its POWER switch to the I (on) position.

Place the target table so that its grid is located approximately 1.2 m from theRotating-Antenna Pedestal, as shown in Figure 3-4. Make sure that themetal rail of the target table is correctly aligned with the shaft of theRotating-Antenna Pedestal.


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Figure 3-4. Position of the Rotating-Antenna Pedestal and target table.

G 6. Calibrate the Tracking Radar Training System according to the instructionsin sections I to V of Appendix B.

In LVRTS, decrease the Clockwise and Counterclockwise FrictionCompensation settings by about 10%. This should provide good radarperformance while allowing convincing demonstrations of asynchronousinverse gain jamming to be performed, using either noise or the repeatedecho signal.

Set the RF POWER switch on the Radar Transmitter to the STANDBYposition.

Make sure that the Tracking Radar is adjusted as follows:

Operating Frequency . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 9.0 GHzPulse-Repetition Frequency . . . . . . . . . . . . . . . . . . . . single, 288 HzPulse Width . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1 nsObservation Range . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3.6 m

Asynchronous Inverse Gain Jamming Set Up

G 7. Remove the small metal plate target, used for the Tracking Radarcalibration, from the target table mast.

Turn off the target table. Move the metal rail to either end of the target table.The metal rail will not be used during the exercise.


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Place the Radar Jamming Pod Trainer support (part number 9595-10),provided with the Connection Leads and Accessories, onto the target table.Position it so that it is in the center of the target table grid.

G 8. Make sure that a 50- load is connected to the Radar Jamming Pod TrainerCOMPLEMENTARY RF OUTPUT.

Install the Radar Jamming Pod Trainer onto its support (in the horizontalposition) using the short support shaft (part number 33125).

Align the Radar Jamming Pod Trainer so that its horn antennas are facingthe Tracking Radar antenna and aligned with the shaft of the Rotating-Antenna Pedestal. The longitudinal axis of the Radar Jamming Pod Trainershould be aligned with the shaft of the Rotating-Antenna Pedestal.

Rotate the infrared receiver on the Radar Jamming Pod Trainer toward thedirection from which you will use the remote controller.

Install the Power Supply (Model 9609) of the Radar Jamming Pod Traineron the shelf located under the surface of the target table. Connect thePower Supply line cord to a wall outlet.

Connect the power cable of the Radar Jamming Pod Trainer to the multi-pinconnector located on top of the Power Supply.

G 9. On the Radar Transmitter, depress the RF POWER push button. The RFPOWER ON LED should start to flash on and off. This indicates that RFpower is being radiated by the Dual Feed Parabolic Antenna.

In LVRTS, turn off the AGC of the Radar Target Tracker.

Turn on the Power Supply of the Radar Jamming Pod Trainer. Turn theRadar Jamming Pod Trainer on. Note that the Radar Jamming Pod Trainerstatus indicates that the Repeater is on. Adjust the remote controller settingsto match the Radar Jamming Pod Trainer status (the Repeater is on, all elseis off).

G 10. Make sure the radar antenna axis is aligned with the Radar Jamming PodTrainer. This can be done by observing the O-Scope Display of the TrackingRadar while adjusting the radar antenna orientation so that the amplitude ofthe Radar Jamming Pod Trainer's repeated echo signal is the same for bothpositions of the antenna main beam.

Observing the O-Scope Display, set the Gain of the MTI Processor so thatthe amplitude of the Radar Jamming Pod Trainer's repeated echo signal isapproximately 0.2 V.

Note the range of the repeated echo signal, as read-off from the O-ScopeDisplay.


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G 11. Using the remote controller, turn the Radar Jamming Pod Trainer Repeateroff.

G 12. Retract the Radar Jamming Pod Trainer's target positioning arm and placethe small (10 x 10 cm) metal plate target at its tip (refer to Figure 3-5). Orientthe metal plate target so that it squarely faces the Tracking Radar antenna.The target should be perpendicular to the longitudinal axis of the RadarJamming Pod Trainer.

Figure 3-5. Installing a target on the target positioning arm of the Radar Jamming Pod Trainer.

Using the target positioning arm while observing the O-Scope Display,adjust the distance of the small metal plate target so that the range of itsecho signal matches the range of the repeated echo signal you notedpreviously (refer to Figure 3-6).


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Figure 3-6. Adjusting the target positioning arm of the Radar Jamming Pod Trainer.

G 13. Adjust the orientation of the small metal plate target so that the amplitudeof its echo signal is between 0.1 V and 0.15 V, while trying to have a similaramplitude for both positions of the antenna main beam.

Note: If the echo signal amplitude is less than 0.1 V, replace thesmall metal plate target with a medium-size (15 x 15 cm) metalplate target.

G 14. Using the remote controller, turn the Radar Jamming Pod Trainer Repeateron.

G 15. Slightly readjust the distance of the metal plate target to maximize theamplitude of the Radar Jamming Pod Trainer composite echo signal on theO-Scope Display, while trying to have approximately the same amplitude forboth positions of the antenna main beam.

Using the remote controller, turn the Radar Jamming Pod Trainer Repeateroff.

The metal plate target echo (Radar Jamming Pod Trainer's natural radarecho) on the O-Scope Display should have an amplitude between 0.1 V and0.15 V. Furthermore, the echo amplitude should be similar for both positionsof the antenna main beam.


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Note: If the amplitude of Radar Jamming Pod Trainer's naturalradar echo is low or greatly differs from one antenna main beamposition to the other, slightly readjust the distance and orientationof the metal plate target to obtain the best compromise betweena maximized and balanced composite echo signal when theRepeater is on, and a balanced natural radar echo having anamplitude between 0.1 V and 0.15 V when the Repeater is off.

G 16. In LVRTS, disconnect Oscilloscope probes 1 and 2 from TP1 and TP2 of theMTI Processor. Connect Oscilloscope probe 1 to TP14 of theMTI Processor. The signal at TP14 corresponds to the video output signalof the MTI Processor.

Make the following settings on the Oscilloscope:

Channel 1 . . . . . . . . . . . . . . . . . . . . . . . . 50 mV/divChannel 2 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . OffTime Base . . . . . . . . . . . . . . . . . . . . . . . . . 1 ms/div

Set the Oscilloscope to Continuous Refresh.

Figure 3-7 shows an example of the radar video signal that you mightobserve on the Oscilloscope screen. The Oscilloscope now allows the targetecho signal received for both positions of the antenna main beam to beobserved in the time domain (this type of display is used in Figure 3-2 toexplain inverse gain jamming).

Figure 3-7. Radar video signal observed in the time domain using the Oscilloscope.

AM Noise Jamming

G 17. Make sure that the Radar Jamming Pod Trainer Repeater is turned off.

Lock the Tracking Radar onto the Radar Jamming Pod Trainer's naturalradar echo signal.


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G 18. Using the remote controller, make the following adjustments to the RadarJamming Pod Trainer:

Noise . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . OnFrequency . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 9.0 GHzFrequency Bandwidth . . . . . . . . . . . . . . . . . . . . . . . . . . 0.0 GHzFrequency Modulation . . . . . . . . . . . . . . . . . . . . . . . . . . TriangleAttenuation 1 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 10 dBAttenuation 2 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 20 dB

AM/Blinking . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . OnModulation Frequency . . . . . . . . . . . . . . . . . . . . . . . . . . . 148 HzModulation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Internal

Repeater . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . OffRGPO . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . OffFalse Targets (FT) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Off

The Radar Jamming Pod Trainer is now transmitting an amplitude-modulated spot noise jamming signal toward the radar antenna.

G 19. Using the remote controller while observing the O-Scope Display, slowlydecrease the level of Radar Jamming Pod Trainer Attenuation. Decreasethe level of attenuation until the amplitude of the AM noise jamming burstsrolling off the radar video signal is about twice the amplitude of the RadarJamming Pod Trainer's natural radar echo signal, as shown in Figure 3-8.

Note: It may be difficult to observe the AM noise jamming burstsrolling off the radar video signal when the refresh rate of theOscilloscope is low. If so, temporarily turn the O-Scope Displayoff. This increases the refresh rate of the Oscilloscope, andthereby helps observing the AM noise jamming bursts rolling offthe radar video signal.

Observe the Oscilloscope displaying the radar video signal as a function oftime. Note that the AM noise jamming bursts are rapidly rolling off thedisplay.


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Figure 3-8. AM noise jamming bursts rolling off the radar video signal.

Does the AM noise jamming have a significant effect on the angulartracking? Briefly explain why.

G 20. Using the remote controller, decrease in 1-Hz steps the amplitudemodulation frequency of the Radar Jamming Pod Trainer signal until it isequal to the radar lobing rate (144 Hz). While decreasing the amplitudemodulation frequency, observe the effects of the AM noise jamming on:1) the roll-off rate of the noise bursts displayed on the Oscilloscope, and2) the radar antenna’s angular tracking.

Note: If the target tracking lock is lost while performing this step,increase the Radar Jamming Pod Trainer attenuation levelby 1 dB and lock the Tracking Radar, once again, onto the RadarJamming Pod Trainer's natural echo signal.

Briefly explain the relation between the roll-off rate of the noise bursts in theradar video signal, and the noise jamming amplitude modulation frequency.


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Briefly explain how the rate and the amplitude of the antenna oscillationsvary with the amplitude modulation frequency of the noise jamming signal.

G 21. Using the remote controller, adjust the Radar Jamming Pod Traineramplitude modulation frequency to 143 Hz.

Note: If the target tracking lock is lost while performing this step,increase the Radar Jamming Pod Trainer attenuation levelby 1 dB and lock the tracking radar, once again, onto the RadarJamming Pod Trainer echo signal.

G 22. Make sure that the DISPLAY MODE on the Antenna Controller is set toPOSITION.

This setting will permit you to verify quantitatively the extent of any jamminginduced angle tracking errors, as illustrated in Figure 3-9.

Figure 3-9. Uncertainty in angular tracking due to antenna oscillations.

What is the average angle ( ) over which the antenna tracking direction iscurrently varying?

= degrees


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PRF Agility

G 23. On the Radar Synchronizer, set the PRF MODE to STAGGERED whileobserving the radar angular tracking, and the radar video signal on theOscilloscope screen.

Is staggered PRF an effective EP to AM noise jamming, a form of inversegain jamming? Briefly explain why.

G 24. On the Radar Synchronizer, set the PRF MODE back to SINGLE.

Change the tracking radar lobing rate to 108 Hz, by setting the RadarSynchronizer pulse repetition frequency (PRF) to 216 Hz. While doing this,observe the radar angular tracking, and the radar video signal on theOscilloscope screen.

Describe the effect that changing the tracking radar lobing rate had on thejamming induced antenna oscillations. Briefly explain why.

G 25. Using the remote controller, make the following adjustments to the RadarJamming Pod Trainer:

Noise . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . OffAM/Blinking . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . OffRepeater . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . OffRGPO . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . OffFalse Targets (FT) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Off

The Radar Jamming Pod Trainer is no longer transmitting an amplitudemodulated spot noise jamming signal toward the Tracking Radar antenna.

Momentarily depress the trigger button on the hand controller to unlock theTracking Radar.


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Repeater Asynchronous Inverse Gain Jamming

G 26. Make the following settings on the Radar Synchronizer / Antenna Controller:

PRF MODE . . . . . . . . . . . . . . . . . . . . . . . . . SINGLEPRF . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 288 Hz

Lock the Tracking Radar onto the Radar Jamming Pod Trainer's naturalradar echo.

G 27. Using the remote controller, turn the Radar Jamming Pod Trainer Repeateron.

When the Repeater is turned on, the Radar Jamming Pod Trainer's naturalradar echo and the repeated echo signal combine to form a rather strongradar echo. This strong radar echo signal may cause some antenna huntingto occur. If so, decrease the clockwise and counterclockwise FrictionCompensation settings by about 10%, realign the antenna with the RadarJamming Pod Trainer, and lock the Tracking Radar onto the echo signal.

Note: If, after decreasing the Friction Compensation settings,there is still some antenna hunting, stop it by gently placing yourfingertips on the side of the radar antenna frame.

G 28. Using the remote controller, begin to amplitude (on-off) modulate therepeated echo signal, by making the following adjustments to the RadarJamming Pod Trainer:

Noise . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . OffAM/Blinking . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . On

Modulation Frequency . . . . . . . . . . . . . . . . . . . . . . . . . . . 148 HzModulation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Internal

Repeater . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . OnRGPO . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . OffFalse Targets (FT) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Off

Note that the difference between the amplitude modulation frequency of therepeated echo signal, and the radar’s lobing rate is too great to causesignificant angle-tracking errors.

G 29. Using the remote controller, decrease the amplitude modulation frequencyof the Radar Jamming Pod Trainer repeated echo signal in 1-Hz steps untilit is equal to the radar lobing rate (144 Hz). While decreasing the amplitudemodulation frequency, observe the effects of the repeater inverse gainjamming on: 1) the rate at which the target echo signal (displayed on theOscilloscope) is amplitude modulated, and 2) the radar antenna’s angulartracking.


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Note: It may be difficult to observe the rate at which the targetecho signal is modulated in amplitude when the refresh rate of theOscilloscope is low. If so, temporarily turn the O-Scope Displayoff. This increases the refresh rate of the Oscilloscope, andthereby helps observe the rate at which the target echo signal ismodulated in amplitude.

Briefly explain the relationship between the rate at which the target echosignal is amplitude modulated, and the amplitude modulation frequency ofthe repeated echo signal.

Briefly explain how the rate and the amplitude of the antenna oscillationsvary with the amplitude modulation frequency of the repeated echo signal.

G 30. Using the remote controller, adjust the Radar Jamming Pod Traineramplitude modulation frequency to 145 Hz.

G 31. On the Radar Synchronizer / Antenna Controller, set the PRF MODE toSTAGGERED while observing the radar angular tracking, and the radarvideo signal on the Oscilloscope screen.

Is staggered PRF an effective EP to repeater inverse gain jamming?

G Yes G No

G 32. On the Radar Synchronizer / Antenna Controller, set the PRF MODE backto SINGLE.

Change the tracking radar lobing rate to 108 Hz by setting the pulserepetition frequency (PRF) to 216 Hz on the Radar Synchronizer / AntennaController. While doing this, observe the radar angular tracking, and theradar video signal on the second oscilloscope display.

Is PRF agility an effective EP to repeater inverse gain jamming?

G Yes G No


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G 33. Turn off the Tracking Radar and the Radar Jamming Pod Trainer.Disconnect all cables and remove all accessories.

CONCLUSION

In this exercise, you demonstrated the effects of asynchronous inverse gain jammingagainst a tracking radar by first using an amplitude-modulated noise jamming signal,and then using an amplitude-modulated repeated echo signal. You learned thatasynchronous inverse gain jamming can either introduce a deflection in the radarantenna’s angular tracking, or cause the antenna to oscillate about the trackedtarget’s direction. While implementing this angle deception EA technique against theTracking Radar, you were able to verify the effectiveness of PRF agility, and ofstaggered PRF as radar EP to AM noise jamming as well as repeater inverse gainjamming.

REVIEW QUESTIONS

1. Briefly describe how inverse gain jamming affects the angle tracking loop of asequential lobing radar.

2. Figure 3-3 graphically shows how in certain conical scan radars the scan-with-compensation technique is implemented. What is the purpose of the additionalreceive beam?

3. What is the difference between synchronous and asynchronous inverse gainjamming?


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4. Inverse gain jamming against a sequential lobing radar, can be achieved by arepeater jammer in the following manner. The weaker radar signals received atthe jammer, before being repeated back to the radar, are amplified. The strongersignals, before being repeated back to the radar, are attenuated. Briefly explainif this implementation of inverse gain jamming is done synchronously orasynchronously with respect to the radar lobing rate.

5. Asynchronous and synchronous inverse gain jamming can be renderedineffective against a sequential lobing tracking radar by randomly changing theradar’s pulse repetition frequency (PRF) on a pulse-to-pulse basis. Brieflyexplain why this electronic protection is effective.

Documents

Exercise 3-1 Deceptive Jamming Using Amplitude-Modulated ... · Deceptive Jamming Using Amplitude-Modulated Signals 3-9 During the third part of the exercise, you will observe and