Comm T-25 pinout to PMA 8000G/Users/garytew/Desktop/comm to audio.png

[Tewbert]

Is this pinout correct for connecting the T-25 to the comm input on the PMA 8000? The shield wire on the PMA 8000 side only goes to ground.

THANKS!

 

[Rhino]

Audio is good. Grounding doesn't look right. You should have a common grounding point for all your audio grounds in your aircraft. That's discussed here:

Ground Loops and Noise in Aircraft Systems

Quite a few forum threads and articles have at various times addressed ground loops, and their potential to cause noise or other interference in your avionics system. Simply put, a ground loop occurs when different paths to ground are used. The difference in resistance, or impedance, on those...

forum.flydynon.com

You didn't say where your common grounding point is in your system. Assuming the PMA8000 is your common grounding point, pin 9 on the T-25 should connect to there through the cable shielding.

 

[Tewbert]

I’m not clear on that because Note 4 in the PMA manual says “all shields should be grounded at the audio panel only. Other end remains floating”. I have everything else going to a common ground bus bar connected directly to the battery.

 

[Rhino]

That's why I said I assumed the PMA8000 was your common ground point, because PS Engineering asks for that. Your power grounds can be joined to the battery, but if your audio grounds go there too, you could easily experience ground loops and noise in your audio. That's why the PMA manual says all shields should be grounded there. That's discussed at the link I provided.

 

[Tewbert]

Gotcha. I’ll make sure all audio grounds go to the PMA. Thanks for your help.