Radios becoming unusable - interference from engine.

David Groat

David Groat

Filing Flight Plan
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Groatski
I have a Van's RV-10 that my father and I built and has been flying for over 6 years now. I use noise cancelling Bose headsets, and over the past couple of years it seems as if the noise cancelling is working less and less well.

I finally tracked it down to some sort of interference coming from the engine. When the engine isn't running the com is clear as a bell, but as soon as the engine starts there's an electronic hiss that gets louder the more I rev the engine. Since my last annual inspection (last month) the hiss has become so loud that I can't hear anything over the radio. I must have done something during the annual to make this problem much worse, but I can't think of what it could have been.

Does anybody have any tips or ideas on what I can look for or do to remedy this? I have two radios and the problem is identical on both.

P.S. - On previous post on this website it seems there are a number of people that can't resist making condescending, ******** comments to demonstrate how much smarter they are than everyone else. To those people please do literally everyone else a favor and immerse your head in a bucket of water for at least 30 minutes. Nobody is impressed with you.
 
David Groat said:
noise cancelling is working less and less well.
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Noise cancelling only reduces acoustic noise, not electrical. What you’re describing here...
David Groat said:
I finally tracked it down to some sort of interference coming from the engine. When the engine isn't running the com is clear as a bell, but as soon as the engine starts there's an electronic hiss that gets louder the more I rev the engine.
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...is electrical noise induced by the engine ignition or alternator.

I’d start by checking all grounds, especially the engine ground strap. If that’s not it, move on to shielding. Don’t ignore the shields on your ignition leads, as they become worn and frayed.
 
David Groat said:
P.S. - On previous post on this website it seems there are a number of people that can't resist making condescending, ******** comments to demonstrate how much smarter they are than everyone else. To those people please do literally everyone else a favor and immerse your head in a bucket of water for at least 30 minutes. Nobody is impressed with you.
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Okay, you've been given some useful suggestions. Now can we maintain the fine tradition of POA and begin condescending remarks and general snarkiness?
 
Thank you all, these have indeed been some very useful suggestions. I now go in armed with something resembling a legitimate plan.

Now you may commence with the snarky comments. You've earned it!
 
I've noticed that some posters come around every few years when they need help with something, and don't otherwise participate, even to follow up on their own threads. Sometimes, they'll even use the rare occasion of their coming to ask for help as an opportunity to criticize the forum. On behalf of everyone else, I suggest they stick around and meaningfully participate. ;)
 
Had a similar problem last September. Turned out to be the antenna. Not sure what happened, it's possible some part of the shoulder harness was making contact with it (yes, it's inside the fuselage). Fortunately, the airplane had an older, unused antenna with a connector in a coax that runs right by the cockpit. Switched to the old antenna, and the noise went away.

What to try depends on what you have access to. If you can easily reach the back of the radio, disconnect the antenna coax, and connect a short piece of coax with a "rubber duckie" antenna (the kind that come with hand-held radios). Fire up the engine, and see if the noise is gone (don't transmit, though. SHOULDN'T hurt the radio, but...).

If the noise is gone, then either your antenna or the coax that runs to it is the problem. Re-connect the original coax, and attach the rubber duckie at the far end, where it attaches to the antenna. If the problem returns, the issue is the coax. Otherwise, it's the antenna itself.

Likely, though, you're looking at alternator noise getting into the radio via the DC power connection. Might be a bad diode in the regulator or an issue with the alternator itself. If your setup has an external filter capacitor, replace it. And, to paraphrase the distinguished Half Fast, check the bejesus out of your grounds.

And as he said, the noise-attenuating headsets mitigate the acoustic noise, not the electronic noise. But you might have a ground issue with the headsets or intercom....

Final, ultimate, desperate move: replace the aircraft battery. It acts as a mondo capacitor, and maybe it's getting a bit weak in that regard. When I had my issue, that's one the steps the alternator manufacturer recommended.

Ron Wanttaja
 
I once complained about my audio panel hissing after some avionics work. Turned out the squelch got turned up and it was my mic. I was 100% convinced it was interference from something when revving the engine. Nope, just the engine noise keying up my mic.
 
Lindberg said:
I've noticed that some posters come around every few years when they need help with something, and don't otherwise participate, even to follow up on their own threads. Sometimes, they'll even use the rare occasion of their coming to ask for help as an opportunity to criticize the forum. On behalf of everyone else, I suggest they stick around and meaningfully participate. ;)
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Yes, I am one of those who apparently don't 'meaningfully' participate and only come around when I need help. However, the few times I've asked what I thought were legit questions there's always a number of snarky know-it-alls in the comment section that do nothing useful except throw petty insults in your direction, and this happens more often than it doesn't. I really don't know what motivates these people other than they must be bored and have nobody around them to impress with their vast knowledge and clever wit, and I have no patience with that crap.

I do participate in other pilot forums, but this was an issue I felt I needed to pull in what resources I can, even if I have to resort to listening to 'those' sorts.
 
Probably the alternator, and perhaps the regulator. Ignition noise is more of a crackle than a hiss. A clear whine that varies with RPM is usually the alternator, and whatever filtering is installed isn't working. A bad diode in the alternator will also generate whine at a lower frequency.

The brushes in the alternator will wear, and so can the slip rings they ride on. They can start generating a constant sparking that comes across as a hiss. The regulator, if its the old electromechanical type, has contacts that are constantly opening and closing, and they can make a variety of noises.

There are so many possibilities here that it's impossible to put a finger on exactly the place, but I'd look first at how many hours and years it's been since that alternator was opened up for inspection. And I'd try what someone else suggested: shut the alternator off in flight and see if the hiss stops.
 
Have some ground loop isolation filters installed. My XM receiver had that problem until I plugged in the filters. Works great now.
 
Wait, wait. Did you mention this already and I missed it?
Try a friend's headset first, to rule that out.
 
Let'sgoflying! said:
Wait, wait. Did you mention this already and I missed it?
Try a friend's headset first, to rule that out.
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I have two Bose headsets and both do the same thing. I didn't try the non NC headsets I use for the back seat passengers, but I guess I can see if that makes a difference.
 
If you haven't checked your squelch, you seriously should.
 
Salty said:
If you haven't checked your squelch, you seriously should.
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Or maybe you shouldn't because I'm snarky. Spend a bunch of money fixing it.
 
David Groat said:
P.S. - On previous post on this website it seems there are a number of people that can't resist making condescending, ******** comments to demonstrate how much smarter they are than everyone else. To those people please do literally everyone else a favor and immerse your head in a bucket of water for at least 30 minutes. Nobody is impressed with you.
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The "ignore" button comes in handy to mute people like that. I've used it on more than a couple occasions.

But to be fair to those who get tired of answering Q's, there's a fair number of people on these sites who are "ask-holes". They'll ask a question then spend time challenging all the responses in a condescending manner, forgetting they're the one who can't fix their problem :)

On the note of your issue - I had a similar problem where it was crackling instead of hiss. Scaled with power usage. Not a big issue on ground, was a big issue flying. Turned out to be a dirty connector on the audio panel. Once cleaned it worked beautifully. Avionics shop diagnosed and fixed in less than an hour of work.
 
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