Dynon SV-25-com-x25 distortion

tlower88

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Dec 29, 2021
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Greetings all-my first post here, so I'm hoping someone can help me and maybe has had the same issue I'm having (?)
I have 2 10" Skyview Classic screens and a Dynon SV-25-com-x25 radio in my 2012 Sting S4 light sport.
Whenever I transmit, there's a loud high-pitched squealing noise that's so bad I can't use the radio anymore. After I push the PTT button, there's no noise, but as soon as I say something into the mic, the high-pitched squealing noise starts again.
I've tried a different headset, both pilot and co-pilot headset/input jacks, turned off the intercom, changed the squelch and mic level settings in the Skyview setup menu-no luck.
Dynon support suggested a possible wiring issue but I couldn't find anything there.
Wondering if it might be a bad radio?
Has anyone else had this issue?
Any help would be appreciated.
 

Rhino

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What kind of com/audio panel?
One or two radios?
Is the squeal only on your internal audio, or is it heard by others in your radio transmission?

And yes, it does sound like a wiring problem.
 

tlower88

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What kind of com/audio panel?
One or two radios?
Is the squeal only on your internal audio, or is it heard by others in your radio transmission?

And yes, it does sound like a wiring problem.
It's the SV-com-X25 radio with a ps engineering dual intercom.
Just one radio.
The squeal is heard at the receiving end too (ATC tower).
 

Rhino

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Still sounds like a wiring problem. Not that it couldn't be the radio, but that's less likely. You might try isolating the audio panel just to eliminate it as a possibility.
 

jakej

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As Rhino says - could be a wiring issue.
More importantly for troubleshooting purposes, has this issue always been the from the get go ? If so then it's most likely a wiring issue as stated before.
Which model PS intercom do you have ?
Turn off the intercom as suggested - is the noise still there ?
With the engine running , on the ground, did you turn every electrical device off that you don't need ?
Including lighter & power supply adapter/s & removed them from 12v socket/s ?
Finally - Is the "noise" still there when engine not running or only when running ?
Have to ask the questions as you gave us limited info - troubleshooting remotely is difficult enough but worse without more data ;)
 

tlower88

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Dec 29, 2021
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Thanks Rhino for your thoughts about possibly the wiring being the culprit.
Jakej: I've owned the airplane for a year now, and it seems like almost from the beginning, this distortion/squealing sound would pop up every once in a while and usually happen when on the ground, so I thought it might've been my location (like close to the hangar) causing it.
Lately it's gotten worse and happening more often-still more often on the ground than in the air.
Yesterday, I tried to call the control tower for taxiing instructions and couldn't even use the radio it was so broken up, so I had to taxi back to the hangar without flying.
The intercom is a PS Engineering PM3000. Yes, I tried turning the intercom off and it still squeals when speaking into the mic.
I will try turning of any uneeded electrical devices, including 12v lighter adapters & sockets, and give that a try.
Also, I will check and see if it happens with both engine running and not running, and report back.
Thanks all for your suggestions.
 

Carl_Froehlich

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Aug 22, 2007
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Borrow an antenna analzer and ring out the coax and antenna. This will require connecting the analyzer at the radio end of the feed line. In the process of gaining access to the feed line visually inspect the coax and associated BNC connectors.

A standard ham radio VHF SWR bridge will work if you can’t find an antenna analzer.

If neither are possible, then make a coax jumper to plug into the radio (replacing the aircraft feed line and antenna). Run the coax out of the plane a few feet and terminate in a simple dipole antenna. The dipole uses two lengths of any convenient wire attached to a center insulator (a scrap of fiberglass/wood/etc.). The coax shield connects to one wire, the center conductor the other. After assembly each side of the dipole should be ~23” long. Support the antenna at the ends nylon string or such.

Using this temporary antenna see if your problem is still there.

Carl
 

Rhino

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Not familiar with the Sting, but if you can get to it, you might try simply replacing the antenna cable. Many manufacturers skimp on antenna cables and use cable that's less than optimal, sometimes far less. I recommend using RG-400 cable, and making sure it isn’t routed alongside any other wiring (not bundled) to every extent possible. Antenna cable is a fairly common issue, and replacing it is relatively easy and inexpensive if it's accessible.
 

Rhino

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By the way, turning off the audio panel doesn't truly isolate it, but you can certainly try simpler things before going that far. How simple mostly depends on how difficult it is to get to things.
 

djones

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I recommend you check to see what com transceiver you actually have. There was the old 425, and the new X25. This sort of issue
sounds awfully like a failed SV-COM-425. Find out what you have and contact the support group at support@dynon.com
 

tlower88

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Dec 29, 2021
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Borrow an antenna analzer and ring out the coax and antenna. This will require connecting the analyzer at the radio end of the feed line. In the process of gaining access to the feed line visually inspect the coax and associated BNC connectors.

A standard ham radio VHF SWR bridge will work if you can’t find an antenna analzer.

If neither are possible, then make a coax jumper to plug into the radio (replacing the aircraft feed line and antenna). Run the coax out of the plane a few feet and terminate in a simple dipole antenna. The dipole uses two lengths of any convenient wire attached to a center insulator (a scrap of fiberglass/wood/etc.). The coax shield connects to one wire, the center conductor the other. After assembly each side of the dipole should be ~23” long. Support the antenna at the ends nylon string or such.

Using this temporary antenna see if your problem is still there.

Carl
Thanks for the suggestions Carl.
As it so happens, I've been a ham radio operator for 55 years, so I can definitely put my antenna analyzer on it and check it out, along with the coax feed and connectors-that's right up my alley :) Now that you mentioned this, it almost sounds similar to a problem I've had in my ham radio station before, with RF creeping into the audio chain and causing audio distortion. Might even try an external antenna as well--I'll check it out!
 

tlower88

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Dec 29, 2021
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Not familiar with the Sting, but if you can get to it, you might try simply replacing the antenna cable. Many manufacturers skimp on antenna cables and use cable that's less than optimal, sometimes far less. I recommend using RG-400 cable, and making sure it isn’t routed alongside any other wiring (not bundled) to every extent possible. Antenna cable is a fairly common issue, and replacing it is relatively easy and inexpensive if it's accessible.
Thanks Rhino-I'll check it out
 

tlower88

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Dec 29, 2021
Messages
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I recommend you check to see what com transceiver you actually have. There was the old 425, and the new X25. This sort of issue
sounds awfully like a failed SV-COM-425. Find out what you have and contact the support group at support@dynon.com
Thanks Dynon. I'll see which which radio model I have, and if it's the old 425 version, it might need replacing.
 

tlower88

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Dec 29, 2021
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Well, as Dynon suggested, it appears the radio was indeed the culprit causing distortion in my radio transmissions. I had the old 425 comm radio and changed it out for the newer sx25 and the transmit audio now seems to be just fine.
I appreciate all of the great suggestions here, but was happy I didn't have to start tracking down a bad component in the antenna system.
Although replacing the radio was probably the more expensive fix, it was also probably the easiest one to do.
Also, thanks to Dynon (David) for all of the help and good customer support I got after installing the new radio by helping me to work out some other issues. Dynon has been extremely helpful to me during the past year since I've owned my airplane.
 

thannaegle

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Jun 29, 2010
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Replacing the old 425 with the x25 is the fix for squealing. I replaced 2 old radios.
They were out of warranty before they were installed. I appreciate Dynon had a $ fix for me.
 
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