Radio interference

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Radio interference

Postby 1X99 » Wed Jul 06, 2016 7:48 pm

I posted this in Electrical systems, but someone here may also have some ideas:
Add'l info: The secondary ignition wires range from 13 KΩ to 30 KΩ; normal ? And, yes the handheld was not connected to the airplane system in any way, just located in the cockpit.
viewtopic.php?f=6&t=3049
Steve Craigle Onex 099
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Re: Radio interference

Postby mike.smith » Wed Jul 06, 2016 9:11 pm

1X99 wrote:I posted this in Electrical systems, but someone here may also have some ideas:
Add'l info: The secondary ignition wires range from 13 KΩ to 30 KΩ; normal ? And, yes the handheld was not connected to the airplane system in any way, just located in the cockpit.
http://sonexbuilders.net/viewtopic.php?f=6&t=3049
Steve Craigle Onex 099


So it sounds like you must be getting some serious electrical noise for it to affect a radio that has no wires or antennas running near anything. Electrical systems were black magic voodoo to me, and are still a mystery, so anything I have to offer is grabbing at straws. But I'll grab. Do you have a battery contactor/solenoid? I don't see one in the schematic. Does that mean you have a number of "hot" wires running behind the panel? Some things (shooting in the dark) that might generate enough current to create noise: fuel pump wiring? Tach wiring? Headset jack wiring running in parallel with the radio antenna coax?

I have two AUX power outlets; the kind you have in your car for a cigarette lighter. I don't remember having any static issues from the AUX in the past, but I installed one that had two USB ports and it appears that whenever that one is drawing power, I get radio static now. It's the exact same +/- wires as before. Only the port changed. I only narrowed it down today, so I'm going to try changing to shielded wire. Point being, even things you wouldn't expect, could create a problem.

The only wires I have in my system that are shielded are my mag wires (like you have) and my headset jack wiring.

You said most of your grounds go to a common ground. For the ones that don't you could disconnect them from the airframe and try running temporary ground wires to the ground block to eliminate those as a problem (grounding issues are the most prevalent issue in electrical systems).

You have a lot of quick disconnects. You might try disconnecting them one at a time and seeing if you get any improvements.

Where is your antenna located, and how is the coax routed? Is there any other equipment or wiring near the antenna?
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Re: Radio interference

Postby gammaxy » Wed Jul 06, 2016 10:02 pm

mike.smith wrote:I don't remember having any static issues from the AUX in the past, but I installed one that had two USB ports and it appears that whenever that one is drawing power, I get radio static now. It's the exact same +/- wires as before. Only the port changed. I only narrowed it down today, so I'm going to try changing to shielded wire. Point being, even things you wouldn't expect, could create a problem.


A lot of cheap USB charging ports have poorly-implemented switching power supplies that produce broadband radio frequency noise that will degrade radio reception significantly. No amount of shielding the wires is going to matter short of completely enclosing the entire port.

I use the CL-USB-IQ port from here: http://www.commitlift.com/usbchargers.html. It's $75 and requires cutting a rectangle in your panel, but it won't interfere with your radio and it will be able to rapid charge apple and android devices. Some of the cheap ones will work too, but the trouble is finding one reviewed by someone competent enough to know if it produces RFI--I thought I saw mention of a couple viable candidates on the vansairforce site, but can't find the links now.
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Re: Radio interference

Postby mike.smith » Wed Jul 06, 2016 11:12 pm

gammaxy wrote:A lot of cheap USB charging ports have poorly-implemented switching power supplies that produce broadband radio frequency noise that will degrade radio reception significantly. No amount of shielding the wires is going to matter short of completely enclosing the entire port.

I use the CL-USB-IQ port from here: http://www.commitlift.com/usbchargers.html. It's $75 and requires cutting a rectangle in your panel, but it won't interfere with your radio and it will be able to rapid charge apple and android devices. Some of the cheap ones will work too, but the trouble is finding one reviewed by someone competent enough to know if it produces RFI--I thought I saw mention of a couple viable candidates on the vansairforce site, but can't find the links now.


Chris:

Thanks for that input. I'll probably try shielding the wires just because it's easy to do, and see what happens. If not, then it will be time to look for another device. Before this device I had a regular cigarette lighter type outlet and just plugged in an adapter with two USB ports. No static from that.
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Re: Radio interference

Postby mike.smith » Sat Jul 09, 2016 4:56 pm

gammaxy wrote:A lot of cheap USB charging ports have poorly-implemented switching power supplies that produce broadband radio frequency noise that will degrade radio reception significantly. No amount of shielding the wires is going to matter short of completely enclosing the entire port.


You were exactly right! I did some tests today. I have two aux outlets. One is a standard cigarette lighter type. When I inserted a USB adapter and plugged in my tablet (to draw power) everything was fine; no noise. The second outlet is the one I converted to a dedicated dual-USB outlet. When I plugged in my tablet there, NOISE! So I'm going to get a different dedicated USB outlet and give that a try, hopefully tomorrow. Always good to know the problem, since that's half the battle.
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Re: Radio interference

Postby mike.smith » Mon Jul 11, 2016 8:34 pm

More info. I replaced the USB outlet and that appeared to solve the problem. But when I started moving the cord around (the cord from the USB to the device) to certain positions, THAT's what causes the static. If the cords are hanging off to the side of the glare shield everything works OK, but if I lift the cords up toward the canopy or move them toward the front of the glare shield I get static. I tried different cords and they all behaved the same. The static goes away when the radio is receiving or transmitting.
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Re: Radio interference

Postby mike.smith » Tue Jul 12, 2016 10:08 pm

Took a flight tonight and the new USB is working fine. No static. But if I raise the cord 6" or more above the glare shield, then static. But I never need to do that, so problem solved for me.
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