AN/APX-100 Transponder Set

DESCRIPTION - TRANSPONDER SET

The transponder set AN/APX-100 enables the helicopter to identify itself automatically when properly challenged by friendly surface and airborne radar equipment. The control panel, located on the right hand console, enables the set to operate in modes 1, 2, 3A, 4, and test. When computer KIT-1A/C/TSEC ( classified ) is installed, mode 4 is operational. The range of the receiver-transmitter is limited to line of sight transmission since it's frequency of operation is in the UHF band making range dependent on altitude.

CONTROL / INDICATOR	FUNCTION
1. TEST GO	Indicates successful built in test ( BIT ).
2. TEST/MON NO GO	Illuminates to indicate unit malfunction.
3. ANT
TOP	Selects antenna located on top of helicopter.
BOT	Selects antenna located on bottom of helicopter.
DIV	Monitor received signals from both antennas and allows transmission via antenna receiving the strongest signal.
4. RAD TEST switch
RAD TEST	Enables set to reply to TEST mode interrogations.
OUT	Disables the RAD TEST features.
5. MASTER control
OFF	Turns set off.
STBY	Places in warm up ( Standby ) condition.
NORM	Set operates at normal receiver sensitivity.
EMER	Transmits emergency replay signal to MODE 1, 2, or 3/A interrogations regardless of mode control settings.
6. STATUS indicators
ANT	Indicates that built in test ( BIT ) or monitor ( MON ) failure is due to high voltage standing wave ratio ( VSWR ) in antenna.
KIT	Indicates that built in test ( BIT ) or monitor ( MON ) failure is due to external computer.
ALT	Indicates that built in test ( BIT ) or monitor ( MON ) failure is due to altitude digitizer.
7. IDENT-MIC switch
IDENT	Initiates identification reply for approximately 25 seconds.
OUT	Prevents triggering of identification reply. Spring loaded to OUT.
MIC	Not used.
8. MODE 3/A code select switches	Selects and indicates the MODE 3/A four-digit reply code number.
9. MODE 1 code select switches	Selects and indicates the MODE 1 two-digit reply code number.

10. MODE 4/CODE control
HOLD/A/B/ZERO	Selects condition of code changer in remote computer.
11. MODE 4 TEST switch
TEST	Selects MODE 4 BIT operation.
ON	Selects MODE 4 ON operation.
OUT	Disables MODE 4 operation.
12. MODE 4 AUDIO/LIGHT control
AUDIO	MODE 4 is monitored by audio.
LIGHT	MODE 4 is monitored by light.
OUT	MODE 4 not monitored.
13. MODE 4/REPLY	Indicates that a MODE 4 reply is generated.
14. TEST/M-1
TEST/ON/OUT	Selects ON, OFF or BIT of MODE 1 operation.
15. TEST/M-2
TEST/ON/OUT	Selects ON, OFF or BIT of MODE 2 operation.
16. TEST/M-3/A
TEST/ON/OUT	Selects ON, OFF or BIT of MODE 3/A operation.
17. TEST/M-C
TEST/ON/OUT	Selects ON, OFF or BIT of MODE C operation.