NORTHROP GRUMMAN T6MC, User Documentation

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Park Air T6MC Controller Page 5-3 Maintenance
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Transmit Operation
PTT Operation
When a 0 volt keying signal is applied to microphone connector CN2 pin 3, relay RLA energizes. Contact
RLA/1 connects the output of the microphone amplifier circuitry to line transformer T2. Contact RLA/2
places a 0 V potential on the centre-tap of T2 secondary to provide a PTT phantom keying signal.
Relay RLB contacts switch transformer T2 between separate transmit and receive audio lines. The
separate lines are used for 4-wire working.
When PTT is active, a ground potential is applied to D7 cathode causing the front panel Busy indicator
(D8) to light.
Audio Routing
The microphone signal is presented to amplifier IC3a; the gain of IC3a is adjusted by RV1 for optimum
signal level during normal speech. IC3b, Tr1, Tr2, and Tr3 with associated components form a VOGAD
circuit. The input level to IC3b is controlled by the potential divider action of R8 and FET Tr1. The gate
voltage of Tr1 is controlled by Tr2/Tr3 that conduct when the output voltage from IC3b reaches
approximately 1 V. The output level is thereby held constant with input variation in excess of 30 dB.
The signal is then passed to the sidetone amplifier IC2b; the gain of IC2b is set to provide a 0 dBm line
operating level (link LK5 not fitted) or a -13 dBm line level (link LK5 fitted). After filtering, the signal is
applied to the line driver IC8, and through PTT relay contact RLA/1 (energized when PTT is active) to
line transformer T2. From T2, the audio is routed to Facilities connector CN1 pins 1 and 2 (for 2-wire
working) and through relay B contacts RLB/1 and RLB/2 to pins 4 and 6 (for 4-wire working).
Intercom Switching
When the PTT is activated while the Intercom switch S4 is pressed down, relay RLA energizes and
contact RLA/1 connects the output of the microphone amplifier to the lines via transformer T2. However,
the 0 V connection to contact RLA/2 is broken by S4, thus inhibiting the phantom PTT signal from the
lines. Audio is therefore routed to the parallel connected controllers, but no PTT signal is sent.
Use of the Intercom facility does not inhibit the External PTT signal. The intercom cannot therefore be
used when an External PTT signal is connected to the transmitter.