G900X/G950 Installation and Maintenance Manual – Pinouts Page A-37
190-00719-00 Revision D
A.3.11 COM/VOR/ILS/Digital Audio
A.3.11.1 COM/VOR/ILS/Digital Audio Function and Emergency Mode
Activation of COM MIC KEY enables COM MIC AUDIO and causes the transceiver to transmit.
500Ω COM AUDIO and 500Ω VOR/ILS AUDIO are 100 mW audio outputs that are intended to drive a
headset or an audio panel. Digital audio outputs from the GMA 1347 are 3.87 Vrms into 150 ohms.
Momentarily depressing the COM REMOTE TRANSFER button toggles the active and standby COM
frequencies. Momentarily depressing the VLOC REMOTE TRANSFER button toggles the active and
standby VLOC frequencies.
The COM REMOTE TRANSFER input may be used for EMERGENCY operation of the COM
transmitter. If the remote transfer switch is depressed for two seconds, the active COM frequency
changes to 121.50 MHz. Once the emergency frequency is activated through COM REMOTE
TRANSFER, the GIA 63W ignores inputs from the front panel controls for COM selections only. The
pilot may exit this independent mode—restoring COM selection control to the front panel knobs and
buttons—by momentarily depressing the COM REMOTE TRANSFER switch.
When TRANSMIT INTERLOCK is active, the GIA 63W COM receiver sensitivity is decreased. This
input is intended to reduce interference from other transmitters in the aircraft. The TRANSMIT
INTERLOCK input should be connected to the PTT input of other transmitters in the aircraft. If
connected to multiple PTT inputs, these connections must include diode isolation or multiple radios
transmit simultaneously.
For digital audio installations, all of this information is transferred in the digital audio data stream.
A.3.12 Com/VOR/ILS/DIGITAL Audio Electrical Characteristics
A.3.12.1 Com Mic Key
Pin Name Connector Pin I/O
COM MIC KEY P601 4 In
INACTIVE: 10 Vin 33VDC or Rin 100k
ACTIVE: Vin 1.9VDC with 75 uA sink current, or Rin 375
Sink current is internally limited to 200 uA max for a grounded input
A.3.12.2 Com Mic Audio, Intercom Mic Audio
Pin Name Connector Pin I/O
INTERCOM MIC IN HI P601 5 In
INTERCOM MIC IN LO (GROUND) P601 6 --
COM MIC AUDIO IN HI P601 7 In
COM MIC AUDIO IN LO (GROUND) P601 8 --
COM MIC AUDIO and INTERCOM MIC each have a 520 Ω AC input impedance and supply the
microphone with a 9 V bias through 620 Ω.
COM MIC AUDIO is set in the factory for 275 mV
RMS
to modulate the transmitter at 80% nominally.
The microphone gain adjustment is accessible through the top cover.
When a 125 mV
RMS
signal at 1000 Hz is applied to the INTERCOM MIC input, the level on the COM
AUDIO output is not less than 7.07 V
RMS
.
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