Radio noise, request troubleshooting help

[bscycleman]

I have a radio noise that I need help with. When I press the PTT and transmit on the Dynon radio what I hear is a muffled echo in my headset. It gets worse when the engine is running and becomes horrible with the engine at full power. Any advice you can offer is greatly appreciated.

Here’s the backstory:
My original setup was a single HDX screen, Dynon radio with the 425 transceiver, and Dynon intercom. I recently added an Avidyne IFD440 and a switch for the PTT select between the two radios. After the upgrade I couldn’t use the Avidyne radio since the Dynon radio would pick up the transmission, even on different frequencies, and garble what I heard in the headset. The Dynon radio was clear as could be, as it had always been. All of the audio wires are shielded, grouped, and grounded per the Dynon and Avidyne manuals.

Dynon exchanged the 425 transceiver for a C25 transceiver. The new transceiver has an additional feature on pin 18, transmit interrupt, that now allows me to use the Avidyne without interference from the Dynon radio. Unfortunately, the Dynon radio now has the problem I described above and is almost useless.

Here’s what I have tried:
Dynon recommended I run a dedicated ground wire from the transceiver chassis to the radio head chassis. There is already a dedicated ground wire in the wire harness, but I tried it anyway with no luck.

I removed the transmit interrupt pin, also with no luck.

I was also getting strobe and alternator whine in the headset. I replace both the battery and alternator. This solved those noises but had no effect on the radio problem.

Another change I made during the upgrade was to combine the Dynon radio and intercom on a single fuse. They were previously separate but I was running out of fuse slots with the new electronics. I can’t imagine this would have an impact but offer it up for folks more knowledgeable than myself.

Brian

 

[Raymo]

First, the wire on pin 18 is telling the Dynon radio to not listen when the Avidyne is transmitting. That pin must be wired into the Avidyne transmit interrupt for the same purpose.

Confirm shields are grounded at one end only and all to a common ground near the audio equipment.
Try the test with a different headset and, if you have a co-pilot seat, from those jacks.
Turn off the Dynon intercom and test.
Try the C25 radio in another plane with a similar setup, if possible.

No idea why the replacement of the alternator would have any effect on strobe noise. I suspect something else changed. A failing alternator can cause noise on the intercom, however.

 

[bscycleman]

Just wanted to close the loop in case this helps anyone else. What Finally worked for me was to reset the software setting on the HDX for side tone volume and gain. I set them all to 50%, then slowly walked the side tone volume to 90%. There is still a slight echo, but you have to be listening for it to notice it.