Radio interference

Discussion of aircraft electrical system design, construction, and problems.

Radio interference

Postby 1X99 » Sat Jul 02, 2016 6:26 pm

I'd be test flying my Onex now except the static in the radio reception makes it a little scary. Engine off, the radio (Garmin GTR 200) receives clear as a bell. Start it up, and static makes communication really dicey. I tried disconnecting the stator; no change. I borrowed a hand held radio; same result. My guru suggested using shielded wires throughout the secondary ignition system. Magnetrons already connected with shielded P leads. I've tried it using the individual ignition systems; about the same with either.
Has anyone had a problem like this? Solutions?
I'm working on the suggested fix; will report any improvement.
Steve Craigle TurboOnex 099
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Re: Radio interference

Postby gammaxy » Sat Jul 02, 2016 10:43 pm

It doesn't sound like your ignitions are the problem. If they were, I'd expect the sound you're hearing to change when running off a single ignition. Are you sure both ignitions and switches are working? There's always the chance with a new install that one of the ignitions isn't turning off (probably the primary one).

My secondary ignition has always been extremely quiet. The primary one is noisy, but only really annoying when I'm listening to something like an AWOS 20+ miles away. I assume this is due to the lawnmower spark plug wires, but haven't put much effort into it.

I think shielding throughout the secondary ignition system will be difficult/impossible to do anything worthwhile. You might be tempted to shield the wire to the switch, but it is always at ~12 volts because it's tied directly (through a fuse, etc) to the positive terminal of the battery, so it isn't a source of your noise. The low voltage wires between the coils and the ignition modules are fluctuating, but again, it's only ~12 volts and a long way from anything that matters and they'd be a pain to shield correctly.

Can you describe the sound you describe as "static"? My primary ignition makes a ticking sound. Knowing if the sound changes with engine RPM or whether it sounds like white noise could be helpful in diagnosing the problem.

Do you have a schematic of your system? Did you do anything unusual like install a capacitor or crowbar circuit?

When you used the handheld, did you tie into the aircraft's antenna? Did you try with the microphone left unplugged to rule-out cockpit noise feeding back into the intercom? If the handheld is completely independent of the airplane's electrical system, it really rules out a lot of possibilities and makes things like RF interference from the EFIS, etc., more likely.
Chris Madsen
Aerovee Sonex N256CM
Flying since September 2014
Build log: http://chrismadsen.org
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Re: Radio interference

Postby mike.smith » Sat Jul 02, 2016 10:49 pm

1X99 wrote:I'd be test flying my Onex now except the static in the radio reception makes it a little scary. Engine off, the radio (Garmin GTR 200) receives clear as a bell. Start it up, and static makes communication really dicey. I tried disconnecting the stator; no change. I borrowed a hand held radio; same result. My guru suggested using shielded wires throughout the secondary ignition system. Magnetrons already connected with shielded P leads. I've tried it using the individual ignition systems; about the same with either.
Has anyone had a problem like this? Solutions?
I'm working on the suggested fix; will report any improvement.
Steve Craigle TurboOnex 099


Are you sure it's static? The Sonex cockpit can be quite noisy, so I have to turn my MIC gain down quite a bit or the ambient noise comes in the microphone and makes everything sound scratchy, or like static. What does your radio sound like to radios outside your plane, when you are transmitting?
Mike Smith
Sonex N439M
Scratch built, AeroVee, Dual stick, Tail dragger
http://www.mykitlog.com/mikesmith
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Re: Radio interference

Postby 1X99 » Tue Jul 05, 2016 10:51 pm

mike.smith wrote:
1X99 wrote:I'd be test flying my Onex now except the static in the radio reception makes it a little scary. Engine off, the radio (Garmin GTR 200) receives clear as a bell. Start it up, and static makes communication really dicey. I tried disconnecting the stator; no change. I borrowed a hand held radio; same result. My guru suggested using shielded wires throughout the secondary ignition system. Magnetrons already connected with shielded P leads. I've tried it using the individual ignition systems; about the same with either.
Has anyone had a problem like this? Solutions?
I'm working on the suggested fix; will report any improvement.
Steve Craigle TurboOnex 099


Are you sure it's static? The Sonex cockpit can be quite noisy, so I have to turn my MIC gain down quite a bit or the ambient noise comes in the microphone and makes everything sound scratchy, or like static. What does your radio sound like to radios outside your plane, when you are transmitting?


Mike & Chris:
Thanks for your inputs. Here's my wiring diagram: https://www.flickr.com/photos/scraigles ... 861723053/
M = main bus; A = Avionics bus Most of the grounds are to a common post on the back of the panel. Not shown are the engine instruments & lighting. I have a battery hot wire to the panel mounted battery switch which feeds the main bus through the ammeter. Battery grounds go to the starter mount and firewall.
I found out that my radio has a built in intercom with an auto squelch. I changed the squelch value to 100% and verified by shouting into the mic and hearing nothing in the headset. I also installed shielded wire between the coils & Hall effect sensors. A test run today showed the same problem of static in reception mode. The primary & secondary ignitions are turning off when the switches are activated, and no change in the static is noted. RPM changes likewise have no effect. Disconnecting the alternator also has no effect. If anyone sees something odd in my diagram that might be a source of random noise (my best description of it) I'd consider some troubleshooting modification....
BTW, all this occurs with the Gemini PDF turned off & no GPS installed. Automotive instruments?
I used the handheld radio with its own antenna; same noise.
All goes away with either radio when the engine stops.
1X99
 
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Re: Radio interference

Postby mike.smith » Wed Jul 06, 2016 12:18 am

So the handheld was not connected to the aircraft in any way? Just by being inside the aircraft with it produces radio noise?
Mike Smith
Sonex N439M
Scratch built, AeroVee, Dual stick, Tail dragger
http://www.mykitlog.com/mikesmith
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Re: Radio interference

Postby nwawingman » Wed Jul 06, 2016 9:53 am

The NGK DR8EA spark plugs reduced the noise I was getting from my primary ignition to a level that I can live with.
Rick Wantz - Arkansas
Sonex 367 T/W AeroVee/Aeroinjector - Prince Elliptical Prop < 254hrs
1st Flight 7/13 KOSHX3 Young EaglesX14
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Re: Radio interference

Postby Glenn.hunt » Thu Jul 07, 2016 9:58 am

I too wouldn't dare fly into controlled airspace because of poor radio transmissions. Reception is loud and clear though. I have been chasing these gremlins for a while now so I will share what I have found so far. In talking to a gentleman who services very delicate medical instruments, he told me that grounding was the key. EVERY ground wire from the radio, intercom, mic jacks etc. should go to a ground block that is insulated from the airframe, and connected directly to the battery. I changed my ground wire(s) from the radio only to the battery and got an immediate improvement. I plan on installing the ground block as he suggested and connect the rest of the radio grounds to it. I also put a Pyramid capacitor inline with the radio power supply, and this didn't seem to do much. I plan on changing to the NGK plugs that someone just recommended. These fixes should eliminate any ignition system interference. The next problem to tackle is cockpit noise. The first thing I did was turn down the mic gain on my radio which helped quite a bit. (Icom A-200) The second thing I did was chuck my Headsets Inc ANR headset. The mic on these pick up all of the shrill background noise. The ANR part worked fine, and the mic would be OK in a Piper/Cessna that has more low end rumble, but the Sonex has a higher end noise. The next thing I did came from a CX4 pilot. He said he blocked the surface area on the mic (both sides) by 50% and it made a big difference for him by not picking up so much ambient cockpit noise. So I took my old David Clark 13.4's and blocked the mic and that also helped. Now I am inclined to by a QUALITY ANR headset (Lightspeed, Bose) which have much better mic components. Other Sonex and RV pilots have done this and commented that a new headset alone solved their problem. I will let you all know how this all works out.
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Re: Radio interference

Postby gammaxy » Thu Jul 07, 2016 10:48 am

Glenn.hunt wrote:He said he blocked the surface area on the mic (both sides) by 50% and it made a big difference for him by not picking up so much ambient cockpit noise.


I've also heard of making a leather cover for the microphone with a hole in the front and back like this:
http://www.aircraftspruce.com/pages/av/ ... ries11.php

I have the Headsets Inc DRE 6001 and am very happy with it, but would like to try the leather cover trick to see if it allows me to turn the VOGAD setting on my MGL v6 down a little.
Chris Madsen
Aerovee Sonex N256CM
Flying since September 2014
Build log: http://chrismadsen.org
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Re: Radio interference

Postby Darick » Mon Oct 31, 2016 7:49 pm

I feel stupid asking this but...
I'm in the process of hooking up the primary ignition switch with shielded wire. Center wire goes to switch terminal using spade crimp-on connector (nothing new here it's just like all the other switches), other end goes to the P lead.

I don't know how to handle the shield wire the best way...connect it to my "forest of tabs" which is located on the inside firewall? I know only one end is to be connected.

If yes, does anyone know if a picture or video exists showing a good technique for attaching the braided shield to a connector? Then what? You would have to extend that connector to the "forest of tabs" with another wire. Seems messy and not very elegant...not that wiring is elegant but I'm a neat freak.

I need a jump start with this.
Darick Gundy
Sonex #1646
N417DG
Taildragger, Aerovee, center stick, Prince P-Tip Prop
MGL E1, F2, V6 radio, Sandia Xponder, Reserve lift indicator (AOA), iFly 520
First flight! 10/21/2017
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Re: Radio interference

Postby Bryan Cotton » Mon Oct 31, 2016 8:30 pm

Darick,
The big boys use these things to terminate shields:
http://m.aircraftspruce.com/catalog/elp ... ecfer=6487

Crimp a lug on the wire and screw that down by the switch.
Bryan Cotton
Poplar Grove, IL C77
Waiex 191 N191YX reserved
Taildragger, Aerovee, acro ailerons
dual sticks with sport trainer controls
Prebuilt spars and machined angle kit
Working panel
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