Troubleshooting SV-COM-T25 Constant Static Sound

[jaredyates]

I have a new installation of a new SV-COM-T25 in a Skyview system. When I first wired it up and tested it, all was well. I secured my bundles and took it for a test flight, and for that flight and ever since, I get a constant static sound on the radio. The "rx" displays on the panel. If I push the volume knob to turn off the squelch, the display changes to reflect that but there is no change to the sound.

I see in the Skyview menu on the screen that there is a squelch adjustment in percentage. Some things that aren't clear to me and that I haven't been able to discern by experimenting are, does a higher number mean a higher threshold, or vice versa? Most Skyview settings are executed upon exiting the menu. Is this one like that too, or is it a real-time adjustment? So far no adjusting of that knob seems to have any impact on the static sound, regardless of being in the menu or exiting it. I haven't been able to find any answers to these questions in the documentation yet.

My troubleshooting has been based on the feedline and antenna, because if I disconnect the feedline from the radio, the sound stops. If I connect the feedline to the radio but disconnect it from the antenna, the sound stops. To me this seems to indicate that the problem is not in the feedline, but just to be sure, I did construct a second feedline (rg400, BNC-TNC) and saw no change. I suspected that because the problem came with the bundling of the wires, maybe I was getting some EMF problem, so I removed the feedline from the bundle and ran it to the antenna without any proximity to other wires. I ran the coax from the radio to the other antenna which is usually connected to the other radio. The other radio is an Icom A200 which works as it always has. I connected the Dynon radio with an old proven RG50 coax to each antenna. None of this has changed the sound.

Both antennas have been in the airplane and proven on other radios before the upgrade.

I guess I'm about out of ideas, does anyone else have any suggestions? Is there some way to find out what the radio thinks its squelch setting is? I am doubting that it's a software problem because the sound goes away when I disconnect the antenna?

 

[MikeD]

Your tests with connecting/disconnecting the cable and trying a new cable imply that the noise you are hearing is being generated external to the device.

You also noted that the RX indicator is illuminated when hearing the static which would also imply the noise you are hearing is being externally generated and being picked up by the radio.

A few thoughts and questions.

1. Do you have the SV-Intercom-2S installed? If so, shut it off and see if it has any impact on the static
2. Does the static occur when the plane is not running? If it does, I would suspect the radio.
3. With the engine running, do you still hear the static when you shut off the alternator? If the static goes away when you shut off the alternator, I would suspect the alternator
4. Shut off each mag when the engine is running. If shutting off a mag lessens the static, then your mag or ignition harness or plugs could be generating the noise.
5. Turning off the comm squelch will introduce static into the system. It would be good to test the squelch setting at the extremes.

These issues are a pain to debug. Persistence will get you there. Good luck!

 

[jaredyates]

Thank you Mike, I'm using a combination audio panel/intercom from PS Engineering, PDA360EX. I don't think there is a way to disable the intercom without also disabling the audio path, since the Dynon is com 2 and com 1 is the failsafe hard-wired option. The noise occurs whether or not the engine is running, and I did test the alternators on and off. I don't think I did a mag check, they are p-mags. The squelch extremes in the Dynon menu don't seem to be impacting the noise.

 

[MikeD]

Hmmm......

If you connect the same cable and antenna to the Icom A200 you get no static.

If you connect the same cable and antenna to the Dynon radio, you get static. If this is the case, could the Dynon squelch be Inop?

 

[jaredyates]

I wondered if there was some software problem keeping the radio from receiving the squelch setting, but then if the antenna is removed, the noise also goes away. Perhaps the antenna is required to receive the ambient RF waves that are making up the static sound? I don't guess there is any way to see the squelch setting that the radio is actually using?

 

[MikeD]

I only have a few hours on my panel but I believe when you change the squelch setting by pressing the volume knob, an indicator will be temporarily displayed in the comm panel window that reflects the squelch setting.

 

[Rhino]

If you get the noise even with the engine off, the problem isn't the alternator or mag.

If you don't get the noise on the A220 when switching cable/antenna, they are likely not the problem.

This leaves you with the radio and audio/radio wiring. Unfortunately that's the toughest to troubleshoot. First, yes, a higher number means a higher squelch threshold. If you set it to max, does the noise go away? If not, you may have a faulty radio.

 

[RV8JD]

Do you have a USB charger plugged in somewhere? Many are known to create static.

 

[jaredyates]

Thanks for the help everyone. I heard back from tech support and they said maybe it requires exiting the menu to save the squelch, and maybe it requires a power cycle. "So the squelch setting in the com radio setup menu doesn't actually change until you exit setup. It may also need the radio to be power cycled, but I have never had to do that." Is it possible to get in touch with anyone at Dynon who actually knows how their stuff works? This information gap is the root of any complaints I have about Dynon. Somebody knows, but the manual doesn't know, and tech support doesn't know. I'm not positive that I attempted a power cycle, so before I can say for sure, I need to test that. No USB chargers but thank you for the suggestion. It sounds like I'm on track for an RMA, it just seems so odd that it was working on the initial test and then quit.

 

[Kevin D]

Jared,

I initially had questions with respect to my T-25 as my primary radio. Not as clear as the G in the second slot.
Background Static as you indicate and it would go away when I transmitted.

I did adjust the software gains and most static went away. When out of the hangar it is totally quiet. Equally satisfied with it and the G #2.
I am a newbee to all this high tech stuff but have always adhered to the rule. After any change Exit the menu, back out of the "system" Shut everything down, reboot one display at a time and then turn on individual components. Never had any failures to Upload or boot and operate correctly.
This weekend to the plane I will check my gain setting.

Kevin D
#272

 

[owenssonex]

It is a long shot, but have you tried changing the receive frequency? I had a 2018 model T25 that had static and showed the receive light on for certain frequencies. Dynon replaced the radio with an updated model (still labelled as a T25) that works great. You indicated the problem occurs with the engine running (or not), so it is unlikely- are you using some type of AC/DC power supply for your testing? Just wondering if the power supply is injecting RF?

 

[Rhino]

He gets it with or without the engine running.

 

[owenssonex]

I edited my post. My question was if he is testing with an external power supply (unlikely)

 

[RV8JD]

For clarification of the radio nomenclature, I'll add this:

The SV-COM-C25 is an integrated VHF Com Radio consisting of two modules, the SV-COM-PANEL and the SV-COM-425 transceiver.

The SV-COM-X25 is an integrated VHF Com Radio consisting of two modules, the SV-COM-PANEL and the SV-COM-T25 transceiver.

The SV-COM-X25 replaced the SV-COM-C25 in late 2019.