Page 4-8
GDR 66 Installation Manual
Revision A
190-00303-24
4.5 Audio
When the GDR 66 is in analog voice mode (ARINC 716 Voice), audio from the microphone and audio to
the headset can be transferred to/from the GDR 66 as analog audio or digital audio. If analog audio is used,
the COM MIC KEY* discrete input must be used. If digital audio is used all of this information is
transferred in the digital audio stream.
4.5.1 Analog Audio
4.5.1.1 Com Mic Audio
The GDR 66 provides one microphone audio input. COM MIC AUDIO has a 150 ohm AC input
impedance and supplies the microphone with a 12 V bias through 400
Ω +/− 20%
. COM MIC AUDIO is set
in the factory for 250 mVrms to modulate the transmitter at 90% nominally. The microphone gain is
adjustable during installation to increase the sensitivity to 20 mVrms or decrease the sensitivity to 2.5
Vrms.
4.5.1.2 Com Audio Out
The GDR 66 provides one audio output that is intended to drive a headset or an audio panel. The rated
output is 4.90 Vrms into a 600 ohm load (40 mWavg). A volume control is available during flight to
reduce the output by at least 40 dB to 49 mVrms. COM 600 OHM AUDIO OUT is the summation of the
COM receiver audio and COM sidetone audio.
4.5.1.3 Com Mic Key
The GDR 66 transmits the audio from the microphone (COM MIC AUDIO IN) when the COM MIC
KEY* input is active. The COM MIC KEY* should be connected to the microphones PTT output. COM
MIC KEY* is a non-configurable discrete input conforming to:
Low: 0 VDC < Vin < 3.5 VDC, OR Rin < 375 ohms (active)
High: 8 VDC < Vin < 36 VDC, OR Rin > 100k ohm (inactive)
Table 4-12 Com Mic Audio
Pin Name
Connector
Pin
I/O
COM MIC AUDIO IN HI
P661
7
In
COM MIC AUDIO IN LO (GROUND)
P661
8
--
Table 4-13 Com Audio Out
Pin Name
Connector
Pin
I/O
COM 600 OHM AUDIO OUT HI
P661
9
Out
COM 600 OHM AUDIO OUT LO
P661
10
Out
Table 4-14 Com Mic Key
Pin Name
Connector
Pin
I/O
COM MIC KEY*
P661
4
In
DRAFT