Help with CCS (chronic comm static)

[RV6-O540]

Even though the forums have given me tons of ideas for trouble shooting and solutions over the last few years, I've been working on this comm problem off and on for over a year with no improvement.
No problem with transmit.. ATC and other planes hear me loud and clear 50 miles+. My problem is any signal received has background static that blocks weaker incoming ATC, planes, atis, etc. (Chicago center not amused on my way to OSH) Closer, stronger signals are readable but static is still in the background. I have perfectly clear reception with engine off.

Heres my main comm/electrical equipment list:
QT Halo Headsets
Garmin GMA 327 audio panel
Garmin Sl-30
Garmin GNS 480
XM weather receiver
B&C 60 amp and 20 amp alternators and regulators
Dual Comant antennas belly mounted, grounded through stainless bolts per instructions.

What I've tried:
-All new shielded mag wiring grounded only at mags, Mags have 140 hrs since OH.
-Rerouted RG 58 coax away from high energy wires.
-Have two ground cables and braided ground straps from engine to firewall.
-Added ground cable from battery to sub-panel and grounded everything to a
central tab forest.
- Disconnected aux audio wire(pin 24 on B connector) from GRT EFIS to audio panel.
-Installed Miracle Antenna Smoothie filter on just SL-30
- Readjusted SL-30 internal side tone,squelch, etc

Tests and results:
- Ground and in flight mag checks - no change
- Central grounding to Battery cable - no change
- Smoothie filter- voltage drop shut off SL-30 on transmit. uninstalled
- SL-30 adjustment- no change in RX static but TX and normal
operation is very quite now. No feed back, cant hear strobes, 4 75w landing lights, or pitot heat in system when operated.
- Audio panel shut off - no change, sl-30 and 480 both get RX static
- Alternators off - no change
-
Conclusions and Questions
- Obviously engine related
- I dont believe it's alternator whine, not high pitched following RPMs
- Noise is more of a course, white noise static, somewhat less a low rpms
- Dosent seem to be isolated to one mag with a mag check
- I suspect ignition wires and or plugs, but not sure how its getting in to system. Champion wires and plugs. Runs great, good mag checks,
- I notice previous owner has longer plug wires folded in bundles and zip tied
near mags. Can this cause RF problems?
- Any ideas on isolating radio interference from the ignition?
- What resistance readings should I see when testing plugs and wires?

I would appreciate any insight on this problem as Ive tried just about everything I know and can find on the forums. Thanks ahead of time.

[DakotaHawk]

Bill,

Sounds like you've started looking at some of the common culprits. Here's some other ideas to look at as well.

Have you tried turning your alternator off and running on battery only? If the noise goes away, consider adding an alternator filter.

What type of regulator are you using? Even though you have a B&C alternator, the regulator may be inducing some noise. Check out the B&C external regulator or the Plane Power external regulator. These are both solid state regulators and minimize/prevent the noise made by older style mechanical regulators.

You said that you've already tried the mags, but you may be getting some bleed-over. A magneto filter can help clean up that noise.

I installed a single capacitor that attaches to the positive lead of the battery and to the ground tabs on the firewall. This was done prior to first engine start, and I've never run without it, so I can't say definitively, but I don't have any noise issues on my radio.



Obviously you're not the first person to ever suffer from static. Let us know what you find.

[pilot2512]

Where are you antennas and what type are they? Have you checked the ground for the antennas?

[spriteah]

Put a high value capacitor on the wire to the radio. 4700uf 16+ volt. Thats an idea. If that makes some difference then also put another say 1000uf and see what happens.

Jim
Austec Avionics

To clarify that is on the + (+ on capacitor) to the power to the radio. - on the cap to a common ground - (-neg plane chassis or ground wire on Comm).

[Rainier Lamers]

There are only two ways interference (which can sound like static) can get into a radio:
a) Antenna (i.e. via the receiver)
b) Via one or more attached wires - PTT, intercom/headset, power supply

Switch on radio, open squelch.
Remove antenna.
You should hear a drop in background noise. Not a huge amount but noticeable. If you get almost no change, chances are that either the antenna cable is shorted at the radio side or the core of the antenna cable is not connected. If this is deemed OK and you are also absolutely sure your antenna connection is to spec, you can consider a faulty receiver. This does happen - a avionics shop should be able to test your receivers sensitivity fairly easily.
If you have done the above and the difference is a lot, start turning off all electrical users one by one until you only have the radio left. If any of these is the source you will hear the result of switching off the offending party immediately. The usual culprits are anything digital, worse if a LCD display is used. If you can locate the source this way you can then target a solution without guessing.
You can do this with and without antenna connected and that will tell you how the noise is getting into your radio.

Bottom line: If you switch everything but the radio off and still can't get good RX and your antenna is good (yes, I know - check again) - send the radio to the shop. Perhaps it is deaf.

Rainier
CEO MGL Avionics

[Walt]

Have you tried a different headset?

Like Rainer I would tend to go looking at antenna cables, connections and antenna mounting (best way to mount is no gasket or paint under the antenna mounting base).

[rocketbob]

EMI/RFI problems don't manifest themselves as static. Your problem is either a poor antenna connection or the receiver is out of alignment (poor SINAD - signal/noise and distortion). Connect a good handheld to the same connection at the radio to see if the problem persists.

[Jamie]

A friend had a very similar issue a couple of years back. On a whim we disconnected the antenna coax at both ends and checked it for continuity. Turns out there was a bad crimp on the antenna end that was shorting the braid to the center conductor. It's worth checking if you haven't done so yet.

[RV6-O540]

Thanks guys for all the suggestions! Ive spent hours researching the forums for similar comm issues, but its great to get all this trouble shooting input on my specific problem.
I'll be working through your suggestion this week and I'll keep you posted. Thanks again!

[molson309]

Since this problem only occurs while the engine is running there's one more thing you could try to isolate the problem. I believe you've tried doing a mag check with no difference, but have you tried turning both mags off? If the noise goes away immediately when the ignition is turned off then perhaps you have some kind of corona or other HV leakage problem that's causing radio static. Also, make sure you're using resistor plugs, though now that I think about it is it even possible to get non-resistor aviation plugs?

Check the ignition wiring for signs of chafing and burning, which could indicate high voltage leakage. Even a little leakage can cause a lot of radio noise. I had a huge problem in my RV with radio noise - I had an electronic ignition using auto plugs - until I finally figured out the spark plug boots were dirty. After cleaning them and greasing them with dialectric grease the problem went away.

The P-leads for the magnetos are a known source of ignition noise. There are capacitors that can be added externally to filter this noise out.

Every time I have heard ignition noise it sounds like a rough buzzing sound that, depending on how strong it is, overrides weaker radio transmissions and if powerful enough can break the squelch of the radio. On my RV it started out as only being heard on very distant/weak signals and over time got worse, until it started to be heard over even strong transmissions.

Good luck on your search! My money is on your ignition since you seem to have eliminated the other usual causes of radio noise from a running engine.