9GT

9GT

Well Known Member
Patron
A question for the avionics experts out there: I have the GMA 240 Audio Panel and am using my GTN 650 for primary comm. When I transmit while flying, there is a lot of cabin noise in the side tone,,,so much so that it pretty much drowns out what I can hear I am saying. If I cup the mic and talk, it reduces the cabin noise in the side tone somewhat. Folks tell me I am transmitting loud and clear but the cabin noise in the side tone is very distracting. I can not seem to find anything in the manuals that addresses this issue. Any suggestions? Thanks. Dave
 
What type headset/mic are you using. The issue might be there rather then with the radio or intercom.

George
 
9GT said:
A question for the avionics experts out there: I have the GMA 240 Audio Panel and am using my GTN 650 for primary comm. When I transmit while flying, there is a lot of cabin noise in the side tone,,,so much so that it pretty much drowns out what I can hear I am saying. If I cup the mic and talk, it reduces the cabin noise in the side tone somewhat. Folks tell me I am transmitting loud and clear but the cabin noise in the side tone is very distracting. I can not seem to find anything in the manuals that addresses this issue. Any suggestions? Thanks. Dave
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Hello Dave,

A few questions to start with.

1. How does the intercom sound? The ambient noise is probably relatively low when you break squelch and talk on the intercom because you didn't mention this.

2. Your jacks are probably wired for stereo. What kind of headset are you using and is the mono/stereo switch set for stereo? Some stereo headsets sound really terrible during transmission when set to mono and plugged into a stereo jack. I know my original Zulu headset sounds this way, but sounds great when set to stereo.

The PTT wiring shown in the GMA 240 installation manual uses a method that puts the PTT switch across the MIC tip and MIC sleeve (audio in lo). This is fairly common because it supports the use of a hand mic, even though no one uses those much anymore.

An alternate (and generally preferred) way of wiring the PTT switch is illustrated in the GTR 200 installation manual.

The PTT switch simply grounds the PTT discrete input and does NOT ground the MIC tip.

You can change your GMA 240 wiring in the same manner such that the pilot PTT simply grounds pin 34 (P2401). It is even better if this PTT switch wire is kept outside of the shielded pair going to the MIC jack (again as shown in the GTR 200 manual).

If you think about this, your MIC probably sounds really clear when you are talking on the intercom, so why change and complicate this by grounding the MIC tip when you transmit on the radio? Instead, just activate (ground) the PTT discrete input via separate wiring isolated from the MIC audio.

Just a few things to consider or try. There are also mic gain and radio sidetone adjustments that can be made.

Let us know if you have questions.

Thanks,
Steve
 
The cockpit noise is the same whether I am using my Zulu's set on stereo or my Halo's.
Steve: The intercom function is fine and does not pick-up the cockpit noise,,,,only when I transmit using the PTT.
My PTT wiring is per the GMA 240 install manual and grounds the mic tip to the sleeve. I will re-wire per your suggestions.
I have never messed with the factory mic gain adjustment on my Zulu. It worked fine in my Cessna as is and other planes I have used them in. My squelch setting is set to activate with the mic close to the lips speaking normally.
I thought there might be something I could adjust to make it go away. I have to eventually remove my panel and the avionics rack/trays to re-wire my GTR 225 which I have not been able to use. Something I was not looking forward to but this issue makes that a priority for me now. Thanks for the help!
 
I was getting a loud squeal (feedback) with the factory setting on my GMA 240 while transmitting. As Bob suggests, turning down the side tone adjustment totally eliminated the problem. I use the Zulus, too. Side tone value of 50 seems to be optimum for me, I think originally it was around 100.

David, I went back and checked my notes. The sidetone adjustment is actually made on the GTN650 COM config page. Factory default was a setting of 91 (-17.5 dB). I eventually ended up at a setting of 50, way down from the original 91 setting.

I also lowered my mic gain as well from the original setting of +12 dB to +6 dB.
 
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Yes, I suggest turning down the sidetone/and or adjusting mike gain on the radio.

I had much feedback/distortion in mine as well till I did that. Out of the box it was too high for both adjustments. Even my Icom A210 had to be tweaked for my new setup.
 
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David,
Sounds like your radio stack is about identical to mine. I have had to do all kinds of adjustments to get the sounds I want.
If your intercom is good and the volume while ptt is good then it sounds like an easy "mike gain" adjustment in the GTN.
It is ashame the GTR is not working as comparing the two would be a good check.
 
9GT said:
The cockpit noise is the same whether I am using my Zulu's set on stereo or my Halo's.
Steve: The intercom function is fine and does not pick-up the cockpit noise,,,,only when I transmit using the PTT.
My PTT wiring is per the GMA 240 install manual and grounds the mic tip to the sleeve. I will re-wire per your suggestions.
I have never messed with the factory mic gain adjustment on my Zulu. It worked fine in my Cessna as is and other planes I have used them in. My squelch setting is set to activate with the mic close to the lips speaking normally.
I thought there might be something I could adjust to make it go away. I have to eventually remove my panel and the avionics rack/trays to re-wire my GTR 225 which I have not been able to use. Something I was not looking forward to but this issue makes that a priority for me now. Thanks for the help!
Click to expand...

Hi Dave,

Good to confirm that the intercom audio is clear and this issue is isolated to transmitting on the radio.

I agree with the others that adjusting the sidetone volume would be the first thing to try.

The PTT wiring change would be last on my list of things to try.

Thanks,
Steve
 
OK. I will try the adjustments first. I just want to clarify though that it is not distortion or squealing I hear in the sidetone, it is actual cockpit noise from the engine and wind I am hearing. The volumn of the sidetone is fine. I will still have to eventually do the GTR 225 rewiring work. I hope the adjustments work so I can postpone that until warmer weather arrives. It's still nasty cold here in Michigan!
 
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UPDATE: 03/15/14

I managed to get to the hanger and do some re-configuration on the GTN 650 as suggested by Pat Hatch. I used Pat's settings and test flew the plane. The cabin noise is now gone so thank you everyone for the help! I will re-wire the PTT as g3xpert recommends, along with the GTR 225 when I have some down time. Gotta love the RV-10. My buddy was flying echelon with me in his 185 hp Cozy MKIV to verify my IAS and he told me a couple times to slow down,,,,he could not keep up!
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same here

Have gtn 650 recently installed, with g3x touch. (amongst other things) Short flight, due to some other issues. Comm was so horrible, switched to my old reliable kx155. I don't have the plane at home, as is still being worked. I only have the trainer on pc and don't see this adjustment for side tone. Must just not be in the trainer. Glad this looks to be the issue. I run with zulu 2's, and this sound is magnified. THx, DM
 
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