Radar Warning Discriminator On Mode Display

TM-1-1520-238-10 Helicopter Attack AH-64A Apache Manual
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TM 1-1520-238-10 4-74 FILTER FILTER CONTROL M01-187 Figure 4-22. Radar Warning Discriminator On Mode Display 4.37.4 AN/APR-39(V)1 Self-Test Operation. The self- test checks all RW set circuits except antennas, high-pass filters and detectors in the high band receiver, bandpass filter and detector in the low-band receiver, analysis signal commutator, and high and low-band blanking circuits. The self-test procedure is done before operation and when any malfunction is detected. A self-test display is shown in figure 4-23. a. Self-test procedures are as follows: 1. PWR switch – ON. Panel lights illuminate. 2. DSCRM switch – OFF. Wait 1-minute for war- mup. Monitor display CRT and audio. 3. SELF-TEST button – Press and hold. a. FWD and AFT strobes appear, extending to about the third circle on the display grati- cule, and a 2.5 kHz (approximately) PRF audio is present immediately. b. Within about 6 seconds, alarm audio is present and the MA light starts flashing. c. Display BRIL control – Turn cw and ccw. Strobes brighten (cw) and dim (ccw) as con- trol is turned. Set BRIL control for desired brightness level. FILTER FILTER CONTROL M01-188 Figure 4-23. Radar Warning Self-Test Mode Display d. AUDIO control – Turn between max ccw and max cw. Audio will not be audible at max ccw and clearly audible at max cw. e. SELF-TEST pushbutton – Release. All indi- cations cease. 4. DSCRM switch – ON. 5. SELF-TEST button – Press and hold. a. Within about 4 seconds a FWD or AFT strobe (either may appear first) and a 1.2 kHz (approximately) PRF audio will be pres- ent. NOTE Occasionally, during the period between pressing SELF-TEST and appearance of the first strobe, a distorted dot on the display and intermittent audio will be present. This is not a fault isolation. b. Within about 6 seconds, the other strobe will appear and the PRF audio frequency will double. c. Several seconds later alarm audio will be present and the MA light starts flashing. d. SELF-TEST button – Release. All indica- tions cease. 6. PWR switch – As desired.

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