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  #1  
Old 11-13-2020, 04:33 AM
PH-SCP PH-SCP is offline
 
Join Date: Feb 2005
Location: The Netherlands, Europe
Posts: 158
Default Terrible whistle using Garmin GNC255A

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 !
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Maastricht Airport (EHBK/MST)
The Netherlands
RV-9
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  #2  
Old 11-13-2020, 06:54 AM
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Walt Walt is offline
 
Join Date: Aug 2005
Location: Dallas/Ft Worth, TX
Posts: 5,840
Default

Try turning down the MIC gain in the 255.
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  #3  
Old 11-13-2020, 06:57 AM
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scard scard is offline
 
Join Date: Jun 2005
Location: Cedar Park, TX
Posts: 3,198
Default

Antenna line issues?
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  #4  
Old 11-13-2020, 07:28 AM
Southern Pete Southern Pete is offline
 
Join Date: Jul 2015
Location: England
Posts: 94
Default

Look in the manual under side-tone - its a software function in the set-up menu. Turning it down should help.
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  #5  
Old 11-13-2020, 07:49 AM
PH-SCP PH-SCP is offline
 
Join Date: Feb 2005
Location: The Netherlands, Europe
Posts: 158
Default

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.
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Simon C. Paul
Maastricht Airport (EHBK/MST)
The Netherlands
RV-9
PH-SCP

"Building an aircraft is the male equivalent to giving birth, it only involves more blood and pain "
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  #6  
Old 11-14-2020, 10:52 AM
PH-SCP PH-SCP is offline
 
Join Date: Feb 2005
Location: The Netherlands, Europe
Posts: 158
Default 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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Maastricht Airport (EHBK/MST)
The Netherlands
RV-9
PH-SCP

"Building an aircraft is the male equivalent to giving birth, it only involves more blood and pain "
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