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indications.
21.1.1.6 IFF Caution Light. The IFF caution light
on the RIO’s ladder lights comes on to indicate that
mode 4 is not operative. The light is operative whenever
aircraftpowerison andtheMASTERswitchisnotOFF.
However, the light will not operate if the mode 4 computer
is not physically installed in the aircraft. Illumination
of the IFF caution light indicates that: (1) the mode
4 codes have zeroized, (2) the self-test function of the
KIT-lA/TSEC computer has detected a faulty computer,
or (3) the transponder is not replying to proper
mode 4 interrogations.
Ifthe IFF caution light illuminates, switch the MASTER
switch to NORM (if in STBY) and ensure that the
MODE 4 toggle switch is ON. If illumination continues,
employ operationally-directed flight procedures for an
inoperative mode 4 condition.
21.1.1.9 IFF ZERO CAW. An IFF ZERO CAW is
displayed in the MFD CAW window when a KIT computer
is installed and the mode 4 codes have been
xeroized. The IFF ZERO CAW is only valid ifthe APX-
100 MASTER switch is not OFF. If the MASTER
switch is OFF, the IFF ZERO CAW is displayed regardless
of whether the IFF codes are zeroized or not.
21 .I .2 Altitude Computations. Altitude computations
are performed by the CADC.
The computer outputs are altitude information corrected
for static position error. The synchro output is
supplied to the altimeter providing the crew with a corrected
altitude indication. The digital output from the
computer is applied to the transponderf or transmission
on mode C, coded in increments of 100 feet, and referenced
to 29.92 inches of mercury.
21.2 IFF INTERROGATOR (ANIAPX-76)
The AN/APX-76 provides radar identification of airborne
and surface Mark 10 IFF systems. It operatesin
conjunction with the radar and is automatically turned
on whenever the RDR power switch is placed to any
position except OFF. A minimum warmup time of 3
minutes is required before successful operation or BIT
can be performed. The system requires l l5-Vat from
the main ac bus through the IFF A/A ac circuit breaker
(157) and 28-Vdc from the main dc bus through the IFF
A/A dc circuit breaker (9F6). It is capable of interrogation
and display of modes I, 2,3A and 4, and of displaying
EMERG AND IDENT on the DD. Refer to
NAVAIR 01-F14AAD-IA.
The APX-76 interrogatorc onsistso fan antennaa rray
that is part of the radara ntenna,a control panel,r eceivertransmitter,
switch amplifier, and for mode 4 operation,
an interrogator computer.
The IFF antenna consists of six dipole antennas
mounted on the surface ofthe radarplanaranay antenna.
The antenna azimuth and vertical coverage is the same
as that of the radar antenna except that the beam width
of the APX-76 is 13”. The transmitter operatesa t a fixed
frequency of 1,030 MHz and the receiver operates at a
fixed frequency of 1,090 MHz.
Except for the display of IFF video, the APX-76 is
the same in all modes of radar operation. The radar
analog signal converter provides an IFF pretrigger for
the purpose of synchronizing the IFF and radar. On
receiving the pretrigger from the radar, the IFF synchronizer
generatestr iggers that establisht he timingoftransmission
of challenges and decoded reply video for
display on the DD. With the radar in low PRF, IFF video
is mixed with radar video and displayed in the radar
format. In high PRF, the IFF video isdisplayed in a
B-scan format without radar video.
‘Ihe synchronizer also sends a mode 4 pretrigger to
the interrogator computer.
The interrogatorc omputer generatesm ode 4 intermgations
and interpolates mode 4 replies. Display ofmode
4 is the same as all other modes. The mode 4 codes are
prevented from zeroing when the RDR power switch is
cycled.
21.2.1 IFF Self-Test. Prior to APX-76 operation,
self-test of the unit should be performed. The APX-76
contains a self-test function that provides closed loop
testing in conjunction with the on-board APX-100 (IFF
Transponder)T. o perform the self-test,t he RIO must set
the mode and code switches on the control panel to
correspond with the mode and code switches of the
APX- 100. The APX- 100 must be in NORM or EMER
before performing the test. ‘Ihe RIO may now initiate
self-test by holding the TEST/CHAL CC switch in
TEST for 5 to 10 seconds. Provided both the IFF and the
APX-76 are functioning properly, two horizontal bars
will be displayed across the DD at approximately 4 and
5 miles illumination of the green CHAL light on the
control panel while the switch is being held in the test
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F-14D 飞行手册 Flight Manual 3(41)
