TM 1-1520-238-10
3-68
Table 3-23.
RT-1296/APX-100(V)1(IFF) and RT-1557/APX-100(V)1(IFF) Control and Indicator
Functions – continued
Control/Indicator
Function
MODE 4 CODE
Selector
Selects condition of code changer in remote computer.
A
Selects mode 4 code setting for present period.
B
Selects mode 4 code setting for succeeding period.
HOLD
Retains mode 4 code setting when power is removed from transponder.
MODE 4
TEST/ON/OUT
Determines whether Mode 4 is on, off, or in BIT operation.
MODE 4 AUDIO/
LIGHT/OUT
Enables or disables audio and visual Mode 4 indicators. Visual indicators signify valid replies.
Audible signal indicates the interrogation and reply computers are set to opposite codes.
RAD TEST/OUT
Enables TEST mode.
STATUS ALT
Indicates that BIT or MON failure is due to altitude digitizer.
STATUS KIT
Indicates that BIT or MON failure is due to external computer.
STATUS ANT
Indicates that BIT or MON failure is due to high voltage standing wave ratio (VSWR) in
antenna.
MODE 4 REPLY
Indicates that a Mode 4 reply is generated.
IDENT/OUT/MIC
Controls transmission of I/P pulse.
MODE 1 Selector
buttons
Selects Mode 1 code to be transmitted.
MODE 2 Selector
buttons
Selects Mode 2 code to be transmitted.
MODE 3/A Selector
buttons
Selects Mode 3/A code to be transmitted.
3.17.3 Operation.
CAUTION
Due to possible operating problems of
the (IFF), usage of the UHF radio on fre-
quency ranges 341.325 thru 345.325 is
prohibited while operating the IFF in
MODE 4.
a. Starting Procedures.
If the MODE 2 code has
not been set previously, loosen two screws which hold the
MODE 2 numeral cover, and slide the cover upward to ex-
pose numerals of MODE 2 code switches. Set these
switches to code assigned to helicopter. Slide cover down
and tighten screws.
1. MASTER control switch – STBY. Allow 2 min-
utes for warm up.
