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GTN650 sidetone

jimbo

Well Known Member
Patron
Searched the threads and haven't found the answer to my problem when transmitting. Sometimes my transmission is clear, a lot of times I'm either not getting a sidetone or too loud of a sidetone (hi pitched squeal) that my transmissions become garbled. I'm still investigating and have talked to Garmin, still no solution.

The configuration setup in the GTN under com my settings are as follows:
Com RF squelch: 0% default and have tried 10% no change
Mic gain: +12 dB default
Sidetone Vol: 91 (-17.5 dB) default-have tried other settings also
Sidetone source: "Internal" per Garmin

What have others have used for these settings that has worked?

More Info:
RV9a, GMA 240 audio panel, Com 1=GTN650; Com 2=Icom 210
Ant for Com 1=top turtleneck mounted Cl-121C
Ant for Com 2=bent whip belly mounted Cl-122
Ant Coax=RG400
Never had a problem with my single Icom radio and removed PSEng intercom!

Thanks
Jim
 
transmitting anomolie

If you have a second radio, it might be contributing. What is Comm 2 and the audio panel doing when you hear the interference? Is your audio panel receiving on your second radio when you are transmitting on Comm 1?

I had a similar issue with side tone that came down to my Garmin radio was receiving transmissions from Comm 2 even when not in receive mode and it was causing side tone garbage.

But, my transmission to outside was fine. Only the side tone was affected.
 
If you have a second radio, it might be contributing. What is Comm 2 and the audio panel doing when you hear the interference? Is your audio panel receiving on your second radio when you are transmitting on Comm 1?

I had a similar issue with side tone that came down to my Garmin radio was receiving transmissions from Comm 2 even when not in receive mode and it was causing side tone garbage.

But, my transmission to outside was fine. Only the side tone was affected.

I think at one time I tried transmitting on the GTN650 (com 1) while com 2 was off but I'll double check. I have to start recording my settings and use selections so I remember what I have tried.

Thanks for the idea.
Jim
 
Try switching to 'external' side tone. What software version does your unit have?
 
Searched the threads and haven't found the answer to my problem when transmitting. Sometimes my transmission is clear, a lot of times I'm either not getting a sidetone or too loud of a sidetone (hi pitched squeal) that my transmissions become garbled. I'm still investigating and have talked to Garmin, still no solution.

The configuration setup in the GTN under com my settings are as follows:
Com RF squelch: 0% default and have tried 10% no change
Mic gain: +12 dB default
Sidetone Vol: 91 (-17.5 dB) default-have tried other settings also
Sidetone source: "Internal" per Garmin

What have others have used for these settings that has worked?

More Info:
RV9a, GMA 240 audio panel, Com 1=GTN650; Com 2=Icom 210
Ant for Com 1=top turtleneck mounted Cl-121C
Ant for Com 2=bent whip belly mounted Cl-122
Ant Coax=RG400
Never had a problem with my single Icom radio and removed PSEng intercom!

Thanks
Jim

Hello Jim,

Do you have an ANR headset?

On our RV-7A we have a GTN 750 connected to the COM antenna on top aft of the tip-up canopy, and a GTR 20 connected to the bottom mounted COM antenna.

The GTR 20 always works great (bottom antenna), but the GTN 750 sidetone is sometimes garbled, and I think I know why.

If I look straight ahead and transmit on the GTN COM, the audio sounds fine. If I turn my head to the right where the right Zulu ANR headset cup is facing the COM antenna just a few feet away and transmit on the radio, the headset garbles the audio most, if not all, of the time.

Our RV's don't provide much distance between a top mounted COM antenna and these ANR headsets, so it is possible you see the same issue I do.

Nothing wrong with the GTN, but the headset ANR circuitry can't handle the RF energy from the nearby COM antenna.

You could test this by turning off the ANR when transmitting on the GTN or by swapping the GTN to the bottom mounted COM antenna. Since your ICOM is a lower power radio, there may not be a problem using it on the top antenna.

BTW, when I hear a garbled transmission (happened on last flight), the copilot in the same aircraft using a non-ANR headset does not hear anything unusual, and the GTN sounds fine to him.

Your issue could be something totally different, but just something else to consider.

Steve
 
Try switching to 'external' side tone. What software version does your unit have?

I think I tried that but I'll try again and document it next time. Garmin Tech said that the GMA 240 audio panel controls the the sidetone so set it on internal.

Software version 6.21. I know that's not the latest so I'll be installing the newest version.

Thanks for your input.
Jim
 
I think I tried that but I'll try again and document it next time. Garmin Tech said that the GMA 240 audio panel controls the the sidetone so set it on internal.

Software version 6.21. I know that's not the latest so I'll be installing the newest version.

Thanks for your input.
Jim

I had to go back and look to see what the difference was on internal vs external (see below).

Try turning the sidetone to 0, this is where I have mine set with a GMA245, you really don't need any as the audio panel is actually providing it (I'm sure G3X Steve will correct me if I'm mistaking).

External (Default) The COM sidetone audio that the pilot hears is the demodulated audio signal that is going to the antenna to be transmitted.

Internal The COM sidetone audio that the pilot hears is the audio signal from the headset microphone before it is filtered for transmission.
 
I had to go back and look to see what the difference was on internal vs external (see below).

Try turning the sidetone to 0, this is where I have mine set with a GMA245, you really don't need any as the audio panel is actually providing it (I'm sure G3X Steve will correct me if I'm mistaking).

External (Default) The COM sidetone audio that the pilot hears is the demodulated audio signal that is going to the antenna to be transmitted.

Internal The COM sidetone audio that the pilot hears is the audio signal from the headset microphone before it is filtered for transmission.

Hello Walt,

Jim has a GMA 240 audio panel. As shown on page 2-2 of the Rev. E GMA 240 installation manual, you would need to install internal jumpers to enable the internal sidetone feature on the GMA 240.

By default, the GMA 240 uses sidetone audio provided by the COM radio.

I still want to hear if 1) does Jim have an ANR headset and 2) does the problem go away when ANR is turned off or the bottom mounted COM antenna is used.

Thanks,
Steve
 
Last edited:
Hello Walt,

Jim has a GMA 240 audio panel. As shown on page 2-2 of the Rev. E GMA 240 installation manual, you would need to install internal jumpers to enable the internal sidetone feature on the GMA 240.

By default, the GMA 240 uses sidetone audio provided by the COM radio.

Thanks,
Steve

Thanks for jumping in and setting me straight on the 240 vs 245 Steve!
(any chance we will see a sidetone volume adj on the 245 in the future?)
 
Last edited:
Hello Jim,

Do you have an ANR headset?

On our RV-7A we have a GTN 750 connected to the COM antenna on top aft of the tip-up canopy, and a GTR 20 connected to the bottom mounted COM antenna.

The GTR 20 always works great (bottom antenna), but the GTN 750 sidetone is sometimes garbled, and I think I know why.

If I look straight ahead and transmit on the GTN COM, the audio sounds fine. If I turn my head to the right where the right Zulu ANR headset cup is facing the COM antenna just a few feet away and transmit on the radio, the headset garbles the audio most, if not all, of the time.

Our RV's don't provide much distance between a top mounted COM antenna and these ANR headsets, so it is possible you see the same issue I do.

Nothing wrong with the GTN, but the headset ANR circuitry can't handle the RF energy from the nearby COM antenna.

You could test this by turning off the ANR when transmitting on the GTN or by swapping the GTN to the bottom mounted COM antenna. Since your ICOM is a lower power radio, there may not be a problem using it on the top antenna.

BTW, when I hear a garbled transmission (happened on last flight), the copilot in the same aircraft using a non-ANR headset does not hear anything unusual, and the GTN sounds fine to him.

Your issue could be something totally different, but just something else to consider.

Steve

Thanks Steve, I'll check all that but it might take me a couple days. I have a Zulu 2 ANR headset. One other thing of interest: when I push the volume knob on the 650 to turn the auto squelch off I do hear a fair amount of static. Usually I have the volume on the 650 at about the 60% level.

Another tidbit of info: I also get some squealing from the com 2 radio when I press PTT but at a much reduced level than the 650 com1. Transmissions are heard better but still not ideal. The common denominator between the 2 coms is the GMA240 audio panel, wiring of course, and the headset. I have talked to ZULU tech support and tried all they have suggested. I am anxious to try the reduced mic gain setting and see what effects that has.

Jim
 
One other thing of interest: when I push the volume knob on the 650 to turn the auto squelch off I do hear a fair amount of static. Usually I have the volume on the 650 at about the 60% level.

Jim

Hello Jim,

It is usual, and handy, to hear static when opening up the squelch on a COM radio.

Many of us do this to verify that the COM radio volume is about right before calling the tower to taxi if the channel has been quiet since power-up.

Thanks,
Steve
 
My Zulu Mike Gain was responsible

for my garbled GTN 650 transmissions ---- under the Zulu mike muff is a plug, under which is a tiny screw to turn down mike gain --- worked for me (learned this from another post on VAF).

FYI, the GTN650 has always been "noisier" on receiving, than my straight 430 number two radio. If I want to hear clearly, I use the 430.

Ron
 
I turned down the gain on the GTN650 to -6db. So far since the feedback squeel hasn't repeated itself (although even before the squeel feedback didn't occur on every PTT transmit). I am still trying to find the sweet spot adjustment on the sidetone setting on the GTN. Jury still out.

Jim.
 
Sidetone GTN-650

When I first connected my Lightspeed Sierra ANR Headset to my newly-installed GTN-650 and pressed push-to-talk three years ago, I immediately noticed three things:

1. A high-pitched squeal was present in the headset headphones during transmit. This was immediately cured by reducing both headset volume controls.

2. The sidetone volume during transmit was noticeably higher than the receive volume in the GTN. This was cured by adjusting the mike gain (and maybe some other settings) in the GTN Configuration set-up. (Related to No. 1 above.)

3. The audio level of the high frequencies of the sidetone only was noticeably lower than that on the GNS-430 that the GTN-650 replaced. After speaking with Garmin tech, this is apparently a characteristic of the GTN because the transceiver portion is manufactured by a different entity than that in the GNS.
 
Hello Walt,

Jim has a GMA 240 audio panel. As shown on page 2-2 of the Rev. E GMA 240 installation manual, you would need to install internal jumpers to enable the internal sidetone feature on the GMA 240.

By default, the GMA 240 uses sidetone audio provided by the COM radio.

I still want to hear if 1) does Jim have an ANR headset and 2) does the problem go away when ANR is turned off or the bottom mounted COM antenna is used.

Thanks,
Steve

After a furlough just getting back into it.

I have used my non-ANR headset also and even tho I haven?t heard any squeal during transmitting, sometimes I don?t hear a sidetone.

When I do use my ANR headset it doesn?t make any difference turning my head when transmitting (responding to an earlier probable cause that Steve had mentioned).

Also, one coax isn?t long enough to switch antennas. I would have to slice in an extension. Long story but I replaced the top antenna coax with a new longer one so I could use it with the GTN650 Com thinking that?s the better antenna. I didn?t have to replace it if I planned to use the new bottom antenna with the GTN650.

So am I correct that the internal setting on the GTN650 for sidetone source should be ?Internal? when used with the GMA 240 AP?

This is becoming one of those ?driving me nuts? issues? . Seems like I have tried everything a few times.
 
Has there been any resolution to this issue?

I've had my GTN650 installed for almost two years. In just the past few months I've had issues where the sidetone is garbled when transmitting on certain frequencies. I haven't been able to nail down the exact range, but it seems to only happen between 121.000(ish) and 125.000(ish). Higher or lower frequencies don't seem to have an issue.

I'm using the same Halo headset I've been using for 5+ years. I have made sure my #2 Comm (GTR20) is not set to the same frequency as what I'm transmitting on. I have never heard the recipient of my transmission complain about the quality, so it only seems to be the sidetone. Using a GMA245R remote audio panel.

It's quite annoying to have to use Comm 2 for certain frequencies and constantly be switching back and forth between Comm 1 & 2....I MUCH prefer to use my GTN as the primary transmitter/receiver.

Any thoughts or comments are appreciated.
 
Problem solved

Searched the threads and haven't found the answer to my problem when transmitting. Sometimes my transmission is clear, a lot of times I'm either not getting a sidetone or too loud of a sidetone (hi pitched squeal) that my transmissions become garbled. I'm still investigating and have talked to Garmin, still no solution.

The configuration setup in the GTN under com my settings are as follows:
Com RF squelch: 0% default and have tried 10% no change
Mic gain: +12 dB default
Sidetone Vol: 91 (-17.5 dB) default-have tried other settings also
Sidetone source: "Internal" per Garmin

What have others have used for these settings that has worked?

More Info:
RV9a, GMA 240 audio panel, Com 1=GTN650; Com 2=Icom 210
Ant for Com 1=top turtleneck mounted Cl-121C
Ant for Com 2=bent whip belly mounted Cl-122
Ant Coax=RG400
Never had a problem with my single Icom radio and removed PSEng intercom!

Thanks
Jim


After a lot of adjustments what finally worked is setting the GTN650 internal com settings as Mic Gain -6; Sidetone Volume 50; Sidetone source-Internal
Finally I can hear ATC without all the distortion on my GTN650 Com 1

I just found this sweet spot today so that is why I haven’t replied earlier.

Happy Flying,
Jim
 
Periodically I have issues with static on my transmissions which are related to my new David Clark headsets. It seems the microphone can twist 90° In direction and picks up a lot more background noise. So make sure it’s not a problem with your headset mic and ensure that you were speaking into the mic. YMMV. Marty
 
I know it is not our product but some advice anyway since we do design and make radios.

Your report gives a hint: It's only on certain frequencies. That points solidly to a phenomena we call RF feedback - it is very similar to you standing on a stage with a microphone too close to a speaker. Depending on how close you get a hollow, bathroom kind of sound anywhere up to howling and distortion. The exact effect is somewhat dependent on the design of the transmit chain from microphone to antenna.

So we are getting RF from the antenna feeding back into the audio input of the radio. This can follow a number of paths so trouble shooting is not always straight forward - even worse - can be two or more paths at the same time.
These are (in order of likelihood).

1) Bad antenna match (VSWR). Reflected energy enters your grounds where it easily couples onto the audio circuits.

2) Antenna too close to headset (with poor headset internal wiring/shielding) - this gets worse the more powerful your radio becomes.

3) Incorrect audio wiring techniques. This could fill a few pages but just a few short hints: Ground loops, bad or missing audio cable shields, using the shields as signal conductors (shields should only be connected on one side so no current can flow). Headset sockets making electrical contact to airframe or large parts (grounded or not).

Fixes range from rewiring everything to locating the source of the issue and fixing that or using ferrites over the audio cables to dampen RF. One particularly effective way to nail these issues is to misuse a small audio transformer (see details on how that is done with the mic leads from headsets in our A16 intercom manual).

In situations where the feedback factor is just sub-critical you will find small changes like you are doing (mic gain, levels etc) makes it go away or come back. RF feedback depends on the wavelength of the transmitted signal as well hence the sensitivity to different frequencies.

Hope this assists

Rainier
CEO MGL Avionics
 
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