GTN750 Squelch

AggieMike88

AggieMike88

Touchdown! Greaser!
Joined
Jan 13, 2010
Messages
20,803
Location
Denton, TX
Display Name
The original "I don't know it all" of aviation.
Home Airfield
KDTO (Denton Enterprise)
We recently took delivery of our 1966 Bo V35 back from the avionics shop installing an Aspen1000, GTN750, PMA8000BT, and other panel improvements.

After a few flights, we have discovered that we need to up the squelch level on the GTN COMM1 a few points. As we operate between 500-800ft AGL around KDTO on tower's freq, 119.95, there is another transmission that is enough to break the automatic squelch setting. Resulting in lots of static and a big distraction.

So far, we haven't found how to adjust the squelch level by button pushing on the unit, nor in the provided documentation.

When we use COMM2 (a KX-155), we don't hear the other transmission.

Any suggestions on how we can up the squelch level without returning to the avionics shop?
 
There are a number of firmware updates that are out there to address the open squelch problem.


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Here is one service bulletin

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What version of firmware are you running? The reason I am asking is that there seems to be some still yet to be resolved issues with the units. It is possible that your unit has older firmware and hasn't been upgraded.

Or it has the current version of firmware and it still hasn't been resolved yet.


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Marauder said:
What version of firmware are you running? The reason I am asking is that there seems to be some still yet to be resolved issues with the units. It is possible that your unit has older firmware and hasn't been upgraded.

Or it has the current version of firmware and it still hasn't been resolved yet.
Click to expand...

I just got a response from the shop (Trevor @ TechAero here at KDTO) about the issue. He confirmed
  • we have the most recent version of the firmware installed (2.13 as mentioned above)
  • we have the correct/best shielded cable available for our installation
  • he experiences the same issue on his GTN750 unit in his aircraft.
  • he is reaching out to his Garmin contacts for more info and assistance.

So at least this isn't a unique situation to our aircraft.
 
This may sound odd, but that happens all the time at KLNK. Anywhere near the city and many radios have their squelch open the whole time. So far, the universal fix, every single time has been to shorten the ELT antenna. Maybe a radio guy like Weirdjim could say why that is.


Disconnecting the ELT antenna works to confirm the above.

YMMV.
 
I should mention that Trevor did a better than top shelf job for us and the club is very happy with his work.

Anyone in the region needing avionics work done should definitely reach out to him.
 
There seems to be some issues with certain GTNs out there. I know a number of owners who are experiencing the squelch challenges. Garmin has replaced some of those units and claimed installation issues with others.

My GTN issue is solely based on the problem with range. My 1993 vintage Narco Mark 12D+ always outperforms the GTN. It is really frustrating knowing you spent that kind of money and your old radio is doing a better job.


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Same issue here as what Marauder said. Have a GTN 650 and a King KX-155, and sometimes the King unit will receive loud and clear while the Garmin sits silent. Very frustrating.
 
If any of you are going to Oshkosh, please hound them for us. I suspect there are a number out there.


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I have a similar issue on my 650. I would get momentary squelch breaks randomly. You can adjust the squelch. To do so hold down the home button when you start the unit (avionics on), you will get to a configuration page. Go to the comms page and you will see an adjustment for the squelch.

I adjusted the squelch and it is better. I agree with everyone though that for the money, this shouldn't be happening. If anyone does hassle garmin about it at Oshkosh, I would certainly appreciate a report back on their response.
 
I have the new GTN comm only unit. The 255. Same issue. I have the auto squelch set at 95 (out of 100) and still get intermittent squelch break. I checked and only have firmware 2.01. I've had the unit back to the shop numerous times since the December install, and they've called Garmin and shrugged their shoulders. Now I see this service bulletin about the problem on a website. Pathetic.

Another problem I have with this radio is that when the HID landing light is on or there is something plugged into the cigarette lighter receptacle, like a charger, I get interference, which I did not get in the old KX-155 and do not get now in the other comm - a 430W.
 
I've never seen a case where a Garmin radio outperforms a KX-155. (Unless the 155 is just broken).
 
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