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G3X XM radio static interference

bkthomps

Well Known Member
So here's a head scratcher for you- I have been noticing lately a correlation of static buildup on my airframe (during later part of cruise phase, descent at high speed, or through IMC) the XM Radio audio will build up static, so I have to switch it off

now, interestingly enough, the XM Audio "output" from the G3X is wired to a toggle switch that allows me to use either XM, or my "aux" sound input back to the GMA35

I never get static on the "Aux" input, only XM

Thoughts? Fixes?
 
I think the first place to look is at the xm antenna for a good ground.

correct me if i'm wrong, but the XM pulls down a digital signal, if it had issues with signal- i would get a "pixelation" sound to the music, or a loss of signal on a recurring basis- no? similar to a satellite dish getting rained on
 
Audio....

This sounds more like a low level audio problem than a UHF signal problem.
Do you have static wicks? I may be way off here but you said it's "static".
Does that mean audio noise? Just a WAG....
 
no static wicks on the plane, not much i can do about that now

here's a diagram, i'm going to make sure both ends of this shield are toning out against ground

T6Hm0Wa.png
 
Audio Impedance

Those lines should be a 600 ohm impedance(resistance so to speak). You have a glass ship, nice static builder (like mine will be), hard to get rid of now (wicks), like you said. If it were me I would put 600 ohm resistors on outputs (which does change the level of audio) just in case they are not 600 ohm imp designed.

You show all shields tied together. "Usually" for audio it's tied at one end to ground. But ground in this case (glass ship) may be anywhere.
Did you do the wiring or is this a schematic of what you think it is?

I know in flying near thunderstorms the radios would start to whistle. The pitch would get higher, then stop. The ADF would point to a thunderstorm. Old days, but the audio impedances are still the same today(should be to be legacy).

Ok, here comes the stupid stuff.. It's a glass ship, get some Al foil and let it
"trail" from the window( 3" by 12"). Maybe spray it with a little adhesive so it sticks on the outside. Tie this to the "ground" of the radios main ground. The ground wire can be any size. This should discharge the high voltage stuff.
Hey, this is only a test. It will tell us if we are on the right track.

Just another WAG...John
 
i'll check the resistance, the wiring was done by approach fast stack, so the diagram was provided after the fact

i'll have to check the shield status to see what it ended up being

i can't retrofit wicks without some serious work, it does need it, i've had led indicators glow during descents with storms nearby, it's an issue i'm aware of- but have not lost comms yet or had any serious issues, just nuisances
 
You can eliminate the switch

here's a diagram, i'm going to make sure both ends of this shield are toning out against ground

You can eliminate the switch if you used a switching jack instead. That way if nothing is plugged into the jack, you get XM radio. If you plug something in, it is automatically switched to the aux jack.
 
You can eliminate the switch if you used a switching jack instead. That way if nothing is plugged into the jack, you get XM radio. If you plug something in, it is automatically switched to the aux jack.

The "switch" is hooked up to a hard wired PS engineering CD player/fm radio, it never ever ever has static

This leads me to believe the problem is between the two garmins
 
The "switch" is hooked up to a hard wired PS engineering CD player/fm radio, it never ever ever has static

If that is the case, then you have isolated the problem either to those contacts of the switch that go to the GDU, or to the wiring of the GDU. I'd start there.
 
no static wicks on the plane, not much i can do about that now

here's a diagram, i'm going to make sure both ends of this shield are toning out against ground

T6Hm0Wa.png

Hi Brian,

Sorry to hear you are having this issue.

We are a little gun-shy to comment on a wiring diagram for one of these hub based systems. In the past we have spent time reviewing and commenting on the wiring only to be told "it isn't really wired that way", but here goes.

Some things to consider.

  1. You have a GMA 35 audio panel with two separate music inputs that are selectable via a rather nice user interface on your GTN 750 touch screen, yet there is a music selector switch installed. Wiring each music source directly to each music input on the audio panel with shielded wiring that is properly grounded only at the audio panel is dramatically superior to what is being shown. See page 24-14 of the Rev. V G3X Installation manual for recommended stereo music wiring between the GDU and an audio panel. It also includes wiring for the separate alert audio.
  2. For whatever reason, both of the audio panel music inputs are shown to be wired together. Re-wiring according to 1. above will fix that too.
  3. We know you know this, but others may not. What is shown as GMA-35 (PRO-X) in your diagram is actually a hub box (not the GMA 35) placed inline between the GDU music output and the GMA inputs. It is strongly recommended that your music sources be wired directly to the GMA 35 music inputs and not through a box, other connectors, or a switch. Not sure what the "XM Audio MTLK3" connector is, but we recommend removing it as well.

We have shipped large numbers of G3X and G3X Touch systems with built-in satellite music support since 2009 and we don't recall running into this before, but perhaps there is something unique about the way your plane picks up charge that is affecting this. We hope that making the shield and other wiring improvements will give you clear SXM music, even in the rain.

Thanks,
Steve
 
Steve, thanks for the reply- i'll dig into this and see, including your suggestions to reroute the wires

I know I have asked you guys in the past via email, and i appreciate your replies- i just wanted to see if anyone else had experienced such an issue from a "simple" problem like a shield, before i dig into rewire efforts

I'm also not positive that all of this goes through the hub- i'll inquire for that diagram view
 
  1. You have a GMA 35 audio panel with two separate music inputs that are selectable via a rather nice user interface on your GTN 750 touch screen, yet there is a music selector switch installed. Wiring each music source directly to each music input on the audio panel with shielded wiring that is properly grounded only at the audio panel is dramatically superior to what is being shown. See page 24-14 of the Rev. V G3X Installation manual for recommended stereo music wiring between the GDU and an audio panel. It also includes wiring for the separate alert audio.
  2. For whatever reason, both of the audio panel music inputs are shown to be wired together. Re-wiring according to 1. above will fix that too.
  3. We know you know this, but others may not. What is shown as GMA-35 (PRO-X) in your diagram is actually a hub box (not the GMA 35) placed inline between the GDU music output and the GMA inputs. It is strongly recommended that your music sources be wired directly to the GMA 35 music inputs and not through a box, other connectors, or a switch. Not sure what the "XM Audio MTLK3" connector is, but we recommend removing it as well.

Thanks,
Steve


I dug into this option, and because the GMA35 only allows Music 2 to be heard by passengers, we had to go the switch route for Music 1 which is heard by crew and passengers, if the Music 2 could be heard by all occupants, my switch could go away :confused:

Also, none of this is going through the hub, it's all bare leads that have been terminated- so that part is eliminated
 
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Hello Brian,

I dug into this option, and because the GMA35 only allows Music 2 to be heard by passengers, we had to go the switch route for Music 1 which is heard by crew and passengers, if the Music 2 could be heard by all occupants, my switch could go away

The GMA 35 does not have this limitation.

You may remove the switch and incorrect wiring, wire the 2 music inputs correctly (direct to each GMA 35 music input), and pilot, copilot, and passengers may listen to either music 1 or music 2.

The GTN 750 pilot guide shows how easy it is to distribute both music sources in this manner.

Thanks,
Steve
 
Hello Brian,



The GMA 35 does not have this limitation.

You may remove the switch and incorrect wiring, wire the 2 music inputs correctly (direct to each GMA 35 music input), and pilot, copilot, and passengers may listen to either music 1 or music 2.

The GTN 750 pilot guide shows how easy it is to distribute both music sources in this manner.

Thanks,
Steve


Steve, while i was flying yesterday i noticed in the menus that i can distribute Music 2 to the pilot/crew, so you're right! I think perhaps at the time of my wiring the GMA35 documents had this limitation? I"ll eliminate the switch and wire this up immediately, thanks for the help, maybe this discussion will benefit others too
 
Radio Static

After eliminating all possible causes call the radio manufacturer. I found there was a recall on my main board for my radio. I sent it in for replacement and now it works great. No static.
 
After eliminating all possible causes call the radio manufacturer. I found there was a recall on my main board for my radio. I sent it in for replacement and now it works great. No static.

working on this still, 3 years later....what radio did you have recalled?

EDIT: finally after swapping antennas, cables, etc, this has been solved

The audio bundle cable was close to the fan/heat sink on the back of the GDU screen, when it was zip tied further away, this all went away....very odd, it was not a typical static interference, more of a digital/fragmentation type degradation, like a sat TV losing a signal during a rain storm.
 
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