The transponder system consists of a combined
receiver/transmitter/ control panel (fig. 3-27) located
on the pedestal extension; a pair of remote switches,
one on each control wheel; and two antennas,
located on the underside and top of the fuselage.
The system is protected by the 3-ampere TRAN-
SPONDER and the 35-ampere AVIONICS MAS-
TER PWR No. 1 circuit breakers on the overhead
circuit breaker panel (fig. 2-26).
b. Controls/Indicators and Functions.
(1.) TEST-GO indicator. Illuminates to
indicate successful completion of built-in-test (BIT).
(2.) TEST-MON indicator. Illuminates to
indicate system malfunction or interrogation by a
(3.) ANT switch. Selects desired antenna
for signal input.
TOP. Selects upper antenna,
(b.) DIV. Selects diverse (both)
(c.) BOT. Selects lower antenna.
(9.) IDENT-MIC-OUT switch. Selects
source of aircraft indentification signal.
(4.) RAD TEST-OUT switch. Enables
reply to TEST mode interrogations from test set.
(a.) IDENT. Activates transmission
of identification pulse (1P).
(5.) MASTER CONTROL. Selects system
(a.) OFF. Deactivates system.
warm-up (standby) mode.
(c.) NORM. Activates normal oper-
(d.) EMER. Transmits emergency
(6.) STATUS ANT indicator. Illuminates
to indicate the BIT or MON fault is caused by high
VSWR in antenna.
STATUS KIT indicator. Illuminates to
indicate the BIT or MON fault is caused by external
STATUS ALT indicator. Illuminates
to indicate the BIT or MON fault is caused by the
Figure 3-27. Transponder Control Panel (AN/APX - 100)