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Radio Static only while airborne

bobg56

Well Known Member
I have a Legacy 2010 RV12 with the Garmin SL-40 Radio...on the ground the reception is great, transmits great however in the air I'm getting static interference to the point where it's hard to make out what's being said. My transmissions are good in the air. This issue started a few weeks ago and seems to come and go, I've swapped out head sets, turned off strobes, nothing helps, after I land it's gone, reception is clear. I have ordered the blue capacitor that's mounted to the firewall, I've heard that it's needed when using Rotax engines to avert static interference. Maybe that's the problem but what confuses me is the on ground/inflight difference...anybody experience this?
 
Pull the radio out, spray the electrical connectors with CRC electrical contact cleaner and reinsert, see if that helps.
 
Mags and ignition are places I would look first. Do you have an ignition cable going bad (and energy is sparking across)? Some people recommend removing the spark plug boot, trimming the cable 1/4" and sticking it back on so that there isn't a gap or high resistance there. Do you have a grossly mis-gapped spark plug? With traditional mags the P-leads can be a significant source of noise and usual have a bypass capacitor on them. Not sure about the Rotax mags, though. I am new to Rotax and the RV-12, but am learning fast.

Bob Baggerman
 
this could be a longshot but...

I had a similar issue - drove me nuts until I discovered that the air blowing in through the vent was keeping my headset mic turned on. Constant squelch hissing. Turning the vent so it wasn't pointed at my face cleared the problem.
 
Aside from some lower RPMs, the engine has no idea if its on the ground or in the air. The airframe knows.. it has 100kts of wind going across it.. along with the antenna. I suspect a possible problem with the antenna mount/connector.. or as someone previously stated, a mic that is opening squelch for one reason or another. Try disconnecting the other headset?
 
I have isolated headsets, made sure intercom was off (isolate)...I'll take a look at the antenna mounting, maybe some corrosion on the base...I was also thinking it's possible the other aircraft I was listening to had bad radio's but it was also on the local approach freq. and ATIS as well...the blue capacitor is on its way, I will report back when I find the problem...thanks for the suggestions.
 
The problem was fixed by changing out the blue capacitor, Lookwood has them. I guess as simple as a capacitor is they go bad. Mines is mounted on the firewall using an Adel clamp, I suspect either heat or vibration took it out.
 
this could be a longshot but...

I had a similar issue - drove me nuts until I discovered that the air blowing in through the vent was keeping my headset mic turned on. Constant squelch hissing. Turning the vent so it wasn't pointed at my face cleared the problem.

I had that exact issue.
 
The problem was fixed by changing out the blue capacitor, Lookwood has them. I guess as simple as a capacitor is they go bad. Mines is mounted on the firewall using an Adel clamp, I suspect either heat or vibration took it out.

What is the "blue capacitor"?
 
The blue capacitor is the size of a small juice can. It has positive and negative terminals, the positive is attached to the white wire that doubles in a Y split and the yellow 20 gage wire to the VR...it's made for Rotax engines to eliminate static, it comes with the Rotax electrical schematic showing how to wire it in...it's right out of the Rotax 912ULS M/M...mine is mounted to the firewall. I'm the third owner, the guy before me had it installed because of static. It's made by Mallory..22,000pf 40VDC P/N CGS223U040V3C or 658-1614-77819
Lockwood Aviation has them for around $50
 
The blue capacitor described is more properly called an ‘electrolytic’ capacitor. They use a paste like material for the dielectric, and if any cracks or openings develop in the housing, the paste dries out and then they don’t work properly. Failure of these capacitors is a not uncommon problem in avionics boxes, too.
 
For anyone confused by this thread either now or in the future.....

A standard build RV-12 doesn't have a capacitor mounted on the front side of the firewall.

The capacitor specified in the Rotax installation documentation is built into the switch modules that are mounted in the instrument panel, so there is no need to install a separate capacitor.

In this case, since replacing the extra cap that someone had added solved a problem, perhaps that cap had failed and was actually causing the problem via some type of a ground loop to where just removing it altogether might have solved the problem (just a guess).
 
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This capacitor is sold as a requirement for Rotax engines, I don't know the reason why ... it is NOT the one on the circuit board. Lockwood aviation sells them and shows this exact one on the parts page, it comes with a diagram showing how its wired in, not on the circuit board. I've seen it used on a Sea Ray which has the 912ULS...any further questions, call Lockwood Aviation, they have a help line from around 0800. This obviously is not something that Vans has you install as a builder, the guy I bought the -12 from put it on for radio reception issues, it does work and occasionally fails.
 
The one mounted on the switch module is 22000 uf. It is connected within the electrical system in such a way that it is electrically the same as what is shown in the Rotax diagram.
 
All I can tell you is maybe the one on CB failed and this extra capacitor took it's place...I had a good amount of static to the point of considering it a bit dangerous where as I couldn't hear other pilots, ATIS, ATC...it was $50 well spent.
 
Hey Jack, the Y wire is the two white wires that are on the VR...from the VR they come together as one, I believe it supplies the bus, what was done is that this white wire is cut then you add a ring terminal to each and connect to the positive of capacitor, also the yellow wire from the VR is done this way as well...the negative terminal of capacitor is grounded...you can see how its wired from the Rotax M/M...if you order it you'll get the same diagram...very simple.
 
Hey Jack, the Y wire is the two white wires that are on the VR...from the VR they come together as one, I believe it supplies the bus, what was done is that this white wire is cut then you add a ring terminal to each and connect to the positive of capacitor, also the yellow wire from the VR is done this way as well...the negative terminal of capacitor is grounded...you can see how its wired from the Rotax M/M...if you order it you'll get the same diagram...very simple.

Thank's Bob!
 
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