MGL Avionics User Forum

Good morning

I have a V6 in a BushCat. On most CTAF frequencies (122.7, 122.8, and 122.9) it transmits just fine and side tone during intercom and transmission is good. On most ATC frequencies (118.2, 121.7, 125.7) the transmission sounds way over amplified to the point of unreadable. You can hear how bad it is on the side-tone while transmitting. My usual headset is a Lightspeed Zulu 3, but it does the same thing with a Bose A20. I tried turning the mic gain down to as far as -3.0, but still have the issue. Any thoughts?

That sounds very much like RF feedback. Your transmitted signal is getting back into the mic input of your radio and it gets demodulated there and this completes the feedback loop. Distortion is the first sign of this happening - if the feedback is greater it starts to howl or produce a loud tone.
The cause can have many sources and they can combine.
From lack of shielded microphone leads or incorrectly shielded audio cables (creating unintentional ground loops) to RF based feedback due to bad SWR (strong reflected signals from the antenna back to the radio) due to miss tuned antenna or incorrect antenna ground plane (very common issue in particular with rag and tube, wooden or plastic fuselages).

I have a V16. I don't know whether the gain structure and processing is the same as a V6, but this may help.
By default, the microphone input gains were way too high for both A20 and David Clark and the comms were almost unuseable. Currently, my input gains are -4.75dB and I feel that I can certainly reduce that to nearer -7dB, but it's working well currently so I haven't tweaked further.

Again, assuming V16 and V6 are similar, if your comms voices are louder than your TX voices, the input gain is too high. Lower the better to prevent any stray EMI inducing into the audio path.

Can you see a SWR on transmit with a V6?