GTN 750 sidetone changes with frequency selected

GTN 750 and PMA 9000Ex audio panel.

Sidetone seems to vary with selected frequency. With local approach/departure frequency of 120.75 selected, all is normal. When switching to frequency 130.xx and ?up, then there is very loud sidetone. It sounds asif the mic is open and picks up all the cabin noise. It makes for difficult transmitting. No complaints from ATC.
I am puzzled why it changes with frequency. Hope someone can help. No similar issues with the GNC 255 #2 radio.

Is there a way to enter configuration mode (GTN 750) while in flight to play around with side tone and Mic gain settings?

Also, I cannot find any information about these settings (com, sidetone, Mic gain etc) in any GTN750 manual that I can find on line. Anyone knows where I can find this info?

Thanks.

Johan

Originally this was a design feature...The sidetone would increase with an increase in VSWR.

One of the firmware updates enabled a feature to set the sidetone to a different method:

"Added ?Internal? COM sidetone configuration to improve the audio quality of the COM sidetone"

Brantel said:

Originally this was a design feature...The sidetone would increase with an increase in VSWR.

One of the firmware updates enabled a feature to set the sidetone to a different method:

"Added ?Internal? COM sidetone configuration to improve the audio quality of the COM sidetone"

Click to expand...

Brian,
Does this mean that my GTN might be lacking that feature? Can you guide me how to find out if this software is indeed installed and how to access and adjust it.
Thanks.
Johan

I think it was main board version 6.21 that added this setting.

You must get into the config mode and edit the COM settings to enable this feature.

Sorry I am not near the plane and can?t remember the step by step...

Brantel said:

I think it was main board version 6.21 that added this setting.

You must get into the config mode and edit the COM settings to enable this feature.

Sorry I am not near the plane and can?t remember the step by step...

Click to expand...

I will look tomorrow. I remember from yesterday that there were 2 com settings, one was for sidetone represented by a numeric value, and one for Mic gain in dB. Mic gain was in increments of 6dB, which was set at 12dB. There were others which had no meaning to me.
I assume one cannot adjust these in flight?
Thanks for you replies.
Johan

Dorfie said:

I will look tomorrow. I remember from yesterday that there were 2 com settings, one was for sidetone represented by a numeric value, and one for Mic gain in dB. Mic gain was in increments of 6dB, which was set at 12dB. There were others which had no meaning to me.
I assume one cannot adjust these in flight?
Thanks for you replies.
Johan

Click to expand...

Don't be afraid to call the Garmin Aviation tech line. Those guys are typically very good with their support!

Brantel said:

I think it was main board version 6.21 that added this setting.

You must get into the config mode and edit the COM settings to enable this feature.

Sorry I am not near the plane and can?t remember the step by step...

Click to expand...

I will look tomorrow. I remember from yesterday that there were 2 com settings, one was for sidetone represented by a numeric value, and one for Mic gain in dB. Mic gain was in increments of 6dB, which was set at 12dB. I think there were others which had no meaning to me.
I assume one cannot adjust these in flight?
Thanks for you replies.
Johan

Here's the thread that discusses version 6.21:

http://www.vansairforce.com/community/showthread.php?t=125660&highlight=Sidetone+650

You can see what version you're on by tapping on system / system info from the home screen (going from memory). And Garmin just released 6.41 for download /installation.

To see the sidetone setting enter the config mode (press and hold home key during start) and drill down to the comm settings (again I could be more specific if I was in front of my computer).

Hope that helps.

--Dave--
N102FM

Dorfie said:

I assume one cannot adjust these in flight?
Thanks for you replies.
Johan

Click to expand...

I don't think that there are any restrictions from going into maintenance mode in flight, but I'm sure it's not recommended.

You're going to lose the functionality of the GPS for awhile. Also, please have a safety pilot on board to look out the window while you're fiddling with the settings.