Avionics Work on my NXCub

[lrobichaux]

Tonight's flight I tried having both COM 1 and 2 enabled with MIC 1 active. I definitely get feedback, albeit slight, when transmitting. When I turn off COM 2 it's crystal clear.

Let me know how your change works. Also, are you doing this wiring yourself or having an avionics tech do it?

I had an avionics shop do it. Did you try the same test with MIC2 active with both COM1 and COM2 enabled? I'm going to do a proper test this weekend and load up the video results here.

 

[Neal]

Did you try the same test with MIC2 active with both COM1 and COM2 enabled?

No, it was just a quick test of "do I have the issue" and then just went on my way from there I may reach out to Pete to get my name on the list and also verify my install is subject to the same issue and will keep this thread updated should I do anything. I'm getting ready to head out in my motorhome for a bit so it may not be until later when I'm ready to screw something up again

 

[Neal]

I reached out to Pete and he provided me the attached PDF. It seems there's an earlier option of changing the dip switch on the GMA 245R before making a wiring change. Have you tried this option yet @lrobichaux?

It's not a critical issue but I'm open to making this better as the feedback when transmitting is distracting and concerning albeit minimal, but it's there.

 

[Cactus Charlie]

That more complete write up makes it appear that GTR 20 (COM 2) pin 5 is not wired before the mod.

The correct way to de-sense COM 2 is to correctly wire the TX Interlock (2 wires between COM 1 and COM 2). The TX Interlock should be independent of the audio panel wiring. It is simply COM 1 interlock out to COM 2 interlock in, and COM 2 interlock out to COM 1 interlock in.

Didn't CC provide the schematic for the "as delivered" configuration of dual COM aircraft?

 

[Neal]

Umm, does anyone get schematics other than what's in the AMM? It may be in the EX kit manuals but I haven't and don't plan to hunt for it. COM1 is up front, COM2 and GMA 245R are over the rear seat. Would not be fun wiring.

What is your opinion on the #3 dip switch? I plan to give that a try.

 

[Cactus Charlie]

The schematics in the current AMM do not cover the dual COM installation. They are low resolution copies of the schematics applicable to the basic Exec Glass configuration (No IFR GPS and single GTR 200 as COM 1). I created my own schematics for the addition of the G5 and GPS 175 to my FX-3.

I did some more research and it appears that the GNC 355 has no TX interlock capability. That was very surprising since it is provided on the GTR 20 and GTR 200 radios.

I would expect that COM 1 PTT could be used to drive COM 2 "TX Interlock In" and that may be what the CC mod is intended to do.

I can see no way to de-sense COM 1 when COM 2 is transmitting.