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Noise during transmit

D

dspender

Well Known Member
I have dual G3X touch, GTN750, remote audio. Comm 1 is GTN, comm 2 is GTR20. When I push to talk comm 1 while monitoring 1& 2, there is a loud screech in copilots headset. If I am only monitoring comm 1 no screech. What do I do to stop the screech.
 
Ok so you need to hook up the interlock circuit. Look and see if there is a interlock circuit coming out of the GTN and the com. On the GTN 200 it is pin 4 and 5. One is an output and one is a input. connect the output to the input on the opposite radio and visa versa. This will kill the radio you are monitoring while you transmit. Had the same problem with my new panel. Garbled side tone.
 
The GTN does not have a transmit interlock but the GTR20 does. The GTN mic key line should be tied to the GTR interlock in pin, that should fix your problem.
 
dspender said:
I have dual G3X touch, GTN750, remote audio. Comm 1 is GTN, comm 2 is GTR20. When I push to talk comm 1 while monitoring 1& 2, there is a loud screech in copilots headset. If I am only monitoring comm 1 no screech. What do I do to stop the screech.
Click to expand...

Were you able to stop the screeching sound? I have experienced it just the other day.
 
Keying the mic on one radio is absolutely blasting the other radio's antenna. Temp solution is to only use the monitor function briefly (like getting ATIS while staying with Approach) and turning it off after. The better solution, as mentioned, is to wire the interlock, which temporarily cuts off the Rx on your second comm when you key Tx on the first.
 
I believe we are on the right track here. Again, the screech occurs in the co pilot's headset when I transmit on 1 (the GTN) and am monitoring 1 & 2. If only monitoring 1 while I transmit on one, the copilot hears no screech.

My aerotronics builder suggested I tie into a lead that goes from Pin 12 on my GMA 35 (remote audio) and the GTN750 and run that lead to Pin 5 (Transmit interlock in) on the GTR20 (Comm2). STill screeching. Am I supposed to do something with Pin 4 (Transmit interlock out) on the GTR20?
 
One other confession. My comm antennas are 29 inches apart. Garmin told me they should be further apart. They also suggested I may want to run the coaxials on separate sides of the airframe rather than near each other. Thoughts?
 
Walt said:
The GTN does not have a transmit interlock but the GTR20 does. The GTN mic key line should be tied to the GTR interlock in pin, that should fix your problem.
Click to expand...
Reviving an old thread here, but it seems to fit my issue...

I'm doing a panel upgrade that includes adding a new GTR 200 as Com 1, but I'm keeping my old King KX-125 as Com 2. My issue is transmit interlocks; the GTR 200 has pins for interlock IN and OUT, while the KX-125 has only one pin for interlock IN.

If the radios had dual interlock INs/OUTs, then that seems easy, just wire inny-outie, but with the King radio having only the input, does Walt's statement quoted fit here? As in the GTR OUT pin feeds the King IN pin while the King PTT mic key wire feeds the GTR IN pin... is that how I read this?

Seems simple enough but sometimes I need help to get my thick head around it... thanks!
 
jbDC9 said:
Reviving an old thread here, but it seems to fit my issue...

I'm doing a panel upgrade that includes adding a new GTR 200 as Com 1, but I'm keeping my old King KX-125 as Com 2. My issue is transmit interlocks; the GTR 200 has pins for interlock IN and OUT, while the KX-125 has only one pin for interlock IN.

If the radios had dual interlock INs/OUTs, then that seems easy, just wire inny-outie, but with the King radio having only the input, does Walt's statement quoted fit here? As in the GTR OUT pin feeds the King IN pin while the King PTT mic key wire feeds the GTR IN pin... is that how I read this?

Seems simple enough but sometimes I need help to get my thick head around it... thanks!
Click to expand...

Good Afternoon,

That is correct, COM 2 Mic Key Out from the audio panel will be wired in parallel to the COM 2 Mic Key input on COM 2 and the Interlock Input on the GTR 200. TX interlock in on the GTR 200 is an active low discrete input that de-senses the GTR 200 receiver, in response to the same signal that causes the King radio to transmit.

There is an interconnect drawing for a similar combination of equipment on page D-4 of the GTR 200 Installation manual.

Thanks,

Justin
 
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