Advice please from experts:

Has anyone had any radio issues using the Monroy ATD 300 poor man’s TCAS, with the audio lead plugged into the headset socket?

I have a loud(ish) squeal on radio Tx, and an expert suggested the SPA 400 needed changing, if the squeal disappeared with the IC switched off. It did, and changed the SPA 400. However it still squeals.

Tried a little trouble shooting yesterday, and it seemed the ATD 300 audio plug might be the cause, in that when removed the squeal disappeared. However that was on ground engine off. The alternator is both internally and externally suppressed.

Dom,

 

Take a look at pdf page 16:

 

 

And pdf page 2

 

 

It appears the tip of the Monroy is meant for a speaker (8 ohms) whilst the tip of the intercom is meant for a headphone (300 ohms).  Maybe there is some feed back or inductance mismatch. 

 

I have wired the specific ATD headphone output to the audio input for NAV2 on my TERRA audio panel and I have no feed back whether the intercom is on or not and whether it is switched to the speaker or headphone.  Of course, it is hard wired at the back of the audio panel and plugged into the ATD.