Drawing: Cobra Drawing: Cobra

Radar Warning Set

Drawing: APR 39 indicator

The radar signal detecting set AN/APR-39 provides the pilot with visual and audible warning when a hostile fire-control threat is encountered. The equipment responds to hostile fire-control radars but non-threat radars are generally excluded. The equipment also receives missile guidance radar signals and when the signals are time-coincident with radar tracking signal, the equipment identifies the combination as an activated hostile surface-to-air missile (SAM) radar system. The visual and aural displays warn the pilot of potential threat so that evasive maneuvers can be initiated.

Control/Indicator Function
1. MA indicator Flashing indicates high radar missile threat with DSCRM switch in ON
2. BRIL control Adjusts indicator illumination.
3. NIGHT-DAY control Adjust indicator intensity.

Drawing: APR 39 control panel

4. AUDIO control Adjust radar warning audio volume.
5. DSCRM switch:     


Without missile activity - Provides strobe lines for ground radar and normal audio indications.
With missile activity - Provides strobe lines for ground radar, flashing strobe line (s) for missile activity, and flashing MA (missile alert) light.


Without missile activity - No indications.
With missile activity - Flashing strobe lines for missile activity (no strobe lines for ground radar), flashing MA light, and audio warning.
6. Self Test switch:

with DSCRM switch OFF
PWR switch ON

Forward and aft strobes appear, extending to approximately the third circle on the indicator graticule and 2.5 khz audio present immediately.

Rotate indicator BRIL control CW & CCW

Within approximately 6 seconds, alarm audio present and MA lamp starts flashing.

Rotate control unit AUDIO control between maximum CCW and maximum CW

Indicator strobes brighten (CW) and dim as control is rotated.


Audio not audible at maximum CCW and clearly audible at maximum CW.

Set DSCRM to ON.
Press & hold SELF TEST

All indications cease.
Within approximately 4 seconds a FWD or AFT strobe and 1.2 khz PRF audio present. Within approximately 6 seconds the other strobe will appear and APRF audio will double.
7. PWR switch:


Applies power to radar set


De-energizes radar set.

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Updated: 12 January 2008
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Born on 26 March 1999