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Terrible whistle using Garmin GNC255A

PH-SCP

Well Known Member
Hi Guys,

When 8.33 Khz spacing became mandatory in Europe, I purchased a Garmin GNC255A VHF radio. Also bought a GMA240 audiopanel and kept the SL30 as a second radio.

When using the GNC255A I get a terrible whistle when pushing the PTT button. When I start to talk the whistle reduces but does not go away completely.

I tried every combination on the audio panel but that does not help.
Selecting COM2 (SL30) gives a crisp and clear sound without any whistle.

With the experiment, I think I isolated the problem to the GNC255A but I am no avionics expert. Thought I would give this forum a try for advice.

It sounds as if there is some sort of open loop whereby I re-transmit my own transmission. I pulled out the co-pilots headset too without success.

Is there some sort of internal setting I can tweek to make the whistle go away ?

Thanks in advance !
 
Thanks for the quick replies.
Antenna is not the problem. I switched antenna's between COM1 and 2 and the issue remained the same. I will try "Mike Gain" and "Sidetone" and keep you informed how this works.
 
It worked

Turned the Microphone Gain dowm from 12 to 6 and that took the whistle away. Thanks a lot for your input, happy days ! You guys rock 👍👍
 
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