
Page 4-14 400 SERIES INSTALLATION MANUAL
Page Rev L P/N 190-00140-02
4.7 COM/VOR/ILS AUDIO (GNC 420 AND GNS 430 ONLY)
4.7.1 COM/VOR/ILS 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.
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, GNS
430 and GNC 420 COM transceivers with Mod 2 incorporated 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 GNC 420 or GNS 430 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.
4.7.2 COM/VOR/ILS Audio Electrical Characteristics
4.7.2.1 COM MIC KEY
Pin Name Connector Pin I/O
COM MIC KEY P4002 4 In
This input is considered active if either the voltage to ground is < 1.9 V or the resistance to ground
is< 375 Ω. This input is considered inactive if the voltage to ground is 11-33 V
DC
.
4.7.2.2 COM MIC AUDIO, INTERCOM MIC AUDIO
Pin Name Connector Pin I/O
COM MIC AUDIO HI P4002 6 In
COM MIC AUDIO LO P4002 18 In
INTERCOM MIC HI P4002 5 In
INTERCOM MIC LO P4002 17 In
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
.