Garmin GDR 66 Installatioin Manual

Page 4-8 GDR 66 Installation ManualRevision A 190-00303-244.5 AudioWhen the GDR 66 is in analog voice mode (ARINC 716 Voice), audio from the microphone and audio tothe 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 istransferred in the digital audio stream.4.5.1 Analog Audio4.5.1.1 Com Mic AudioThe GDR 66 provides one microphone audio input. COM MIC AUDIO has a 150 ohm AC inputimpedance and supplies the microphone with a 12 V bias through 400Ω +/− 20%. COM MIC AUDIO is setin the factory for 250 mVrms to modulate the transmitter at 90% nominally. The microphone gain isadjustable during installation to increase the sensitivity to 20 mVrms or decrease the sensitivity to 2.5Vrms.4.5.1.2 Com Audio OutThe GDR 66 provides one audio output that is intended to drive a headset or an audio panel. The ratedoutput is 4.90 Vrms into a 600 ohm load (40 mWavg). A volume control is available during flight toreduce the output by at least 40 dB to 49 mVrms. COM 600 OHM AUDIO OUT is the summation of theCOM receiver audio and COM sidetone audio.4.5.1.3 Com Mic KeyThe GDR 66 transmits the audio from the microphone (COM MIC AUDIO IN) when the COM MICKEY* input is active. The COM MIC KEY* should be connected to the microphones PTT output. COMMIC 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 AudioPin Name Connector Pin I/OCOM MIC AUDIO IN HI P661 7 InCOM MIC AUDIO IN LO (GROUND) P661 8 --Table 4-13 Com Audio OutPin Name Connector Pin I/OCOM 600 OHM AUDIO OUT HI P661 9 OutCOM 600 OHM AUDIO OUT LO P661 10 OutTable 4-14 Com Mic KeyPin Name Connector Pin I/OCOM MIC KEY* P661 4 InDRAFT