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|  MIL-N-81207A(AS)
the external antenna switch on the antenna that provides a minimum
satisfactory signal level for lock-on. In the absence of a usable
signal, the antenna switch shall switch the receiver between the
two antenna ports at a rate of 3 to 6 seconds. An internal solid
state antenna switch will be provided as part of the equipment.
By not grounding the antenna switch enable lead, the switching
circuit shall connect the unit to antenna number one connection.
Built-In-Test - The equipment shall contain
3.5.2.11
built-in-test features that shall provide a positive visual
indication on the airplane cockpit displays if the equipment is
operating satisfactorily. The entire BIT procedure can be
performed from the cockpit without access to equipment not
available in the cockpit. BIT shall provide a confidence level of
approximately 90% of detecting a fault and isolating it to the
WRA. The BIT procedure shall include an interrupting self test
cycle which is initiated by pressing a button on the Control Unit.
When the cycle is initiated, the following functions shall be
checked and the results displayed on the appropriate indicator on
the airplane cockpit.
The Control Unit shall be checked by
(a)
inserting a test word in the Control Unit
and checking to see that it is properly
received by the R\T Unit.
(b) The R/T Unit shall be checked by measuring
various critical signals in the R\T
circuits for an in-tolerance condition
while an internally generated RF TACAN
type signal is present at the receiver
input.
The TACAN System Status shall be checked by monitoring the above
functions. If all are in GO status, the System Status shall be
displayed as a range readout of 0.0 (+0.5, -0.0) nautical mile and
a bearing indication of 180.0 2.5 degrees.
Identity Tone Output - The identity tone output
3.5.2.12
shall be a 1350 Hz signal. The maximum output shall be not less
than 75 mw into a 150 ohm resistive load. The audio output shall
not vary more than 3 dB over an RF input signal range of -90 dBm
to O dBm. Accidental shorting or opening of the output circuit
external to the equipment shall not cause damage to the equipment
or render other functions of the equipment inoperative.
Air-to-Air System Delay - The equipment shall
3.5.2.13
effect an indication to O 0.5 nautical mile in the A\A Mode
when:
(a) The delay at the 50% leading edge
amplitude points of the first transmitted
coded pair of RF interrogation pulses and
37.
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