Can anyone explain EXACTLY how to set up an XCOM 760 transceiver push to talk (PTT) button? I have the PTT lead (7) coming out the 15 pin connector on the back of the radio connected to the PTT metal tab on the microphone jack. Along that wire (connecting #7 to the jack) I inserted one lead going to the PTT switch, and the other lead on the PTT switch goes to ground. The radio receives transmissions well. However, when I press the PTT button, I get a loud squeal and it does not transmit. I have actually set this up completely independent of my airplane’s power system ( I also have a problem getting my MGL radio (V6) to properly work when the airplane engine is on, in that the EFIS and radio work fine with the engine not running, but goes haywire when the engine is on) with a spare battery. Anyway, I would think it should be simple to get the radio to function properly (including the PTT). Everything that is supposed to be grounded is grounded to the negative terminal of the battery, so grounding isn’t the problem,  Any ideas?



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Have you put an SWR meter between the radio and antenna?

No.  What will that tell me specifically about the problem?

Stephen, it’s an overall check that your radio antenna, cabling, and grounding including the antenna mount are satisfactory.

Have you used headphone jack washers that isolate the jacks from the panel / fuselage? They're a specific-purpose washer that feature a "stepped" profile to ensure no part of the jack touches metal.

Yes.  The jacks are isolated.

This is a rough schematic as to how it is wired.  Why doesn't this work?

Swapping headsets and moving between pilot and passenger stations produces no changes?

Right now, it’s just set up for the pilot. If I can get that to work, I’ll wire the copilot jacks. 

Just found this DIY wiring diagram on an XCOM avionics site:  Comparing the below diagram to my above diagram, it looks to me that they are the same (I only wired the pilot jacks).  I guess I'll keep playing with it until it reliably works.

Best get wiring diagram from xcom and I am sure you will what error  causing all problems, been too long since I did one to remember !Tom


On the Xcom site in the education section is a trouble shooting guide, step by step procedures for checking the wiring harness.  See if that will help.

Xcom is out of business now.  I correspond with the owner recently and he said that the email would be shut down shortly.  So I would copy anything off the website that might be helpful in case they shut that down also.


Are you tying all grounds to a common point like a “forest of tabs?” Connecting any of the grounds to an assumed ground like the fuselage may produce issues. I know you stated you tied all grounds to the neg terminal, but just want to make sure HOW you did that. And no, you can’t just tie two grounds together at the panel then run one combined lead to the neg post. I know it sounds stupid but that can cause issues. Electricity is like water in that it takes the path of least resistance. You may be an EE and know that, but WE don’t know what you know! Just trying to help. 

Have you tried removing both jacks from the panel to just hang free?

have you tried a different headset? 

Are you you using an aviation headset? Different impedances could cause a prob. 

These  may seem like simple questions like the computer tech asking if it’s plugged in, but we don’t know. You do appear to have wired it correctly, so we’re now just looking for stupid little nits that could cause issues. 

Last thought. Perhaps recheck the jacks once you remove them WITH the plugs inserted. Make sure the plug doesn’t push one of the other conductors against one of the other leads. 


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