Radio noise/distortion problem

deyoung

deyoung

Line Up and Wait
Joined
Nov 13, 2014
Messages
508
Location
Tucson, AZ
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Display name:
Chris
I'm trying to track down an intermittent problem with radio interference or distortion; any help would be appreciated. You can hear what I'm talking about via the link below.

The problem only happens when I am transmitting; reception is loud and clear. Internal conversation between headsets in the cabin is clean.

I have two KX-155s and a KMA-24 audio panel. The problem happens with both KX-155s equally. It also happens with both PTT buttons, and you hear it on all headsets. When I set the KMA-24 to "INT" you can hear the distortion steadily, when it's happening; when it's set to COM1 or COM2 you only hear it when the PTT is in use. It only appears to happen when the engine is running.

It seems to be intermittent - on my latest flight, everything was clean when we left and for about 45 minutes afterward, then got bad enough to make me switch to a handheld. Once we were on the ground, it wasn't perfect but it was enough better to be readable. I have checked for loose connections and not found any, though I haven't checked the antennas themselves yet because they are hard to get to.

You can hear what I'm talking about here, starting at 12:25. I'm N16279.

http://archive-server.liveatc.net/ktus/KTUS-Del-Gnd-Twr-App-Mar-14-2015-0200Z.mp3

Thanks for any suggestions!!
 
Does the frequency of the noise change with engine RPM?
What sounds troubling to me is the fact that it happens on both radios which have separate amplifiers, cables and antennas.
Logic dictates that the problem should be upstream of the radios, i.e. in the audio panel, wiring, plugs or headset itself.

Did you try a different headset and different connector? (you said that it doesn't matter which PTT so I assume you tried both "sides").

FWIW, what does the ammeter or loadmeter read when this problem occurs? Any rapid oscillations?
 
BigBadLou said:
Does the frequency of the noise change with engine RPM?
Click to expand...

I haven't checked for that specifically---will do the next time I get a chance---but not so obviously that I noticed a difference between cruise and descent (when I wasn't thinking about that specifically, it's true).

Did you try a different headset and different connector? (you said that it doesn't matter which PTT so I assume you tried both "sides").
Click to expand...

Yes---well, I confirmed that my passenger also hears it, using another headset and the co-pilot's headset connectors, obviously. And ATC hears it, so it's not just in the headset system.

FWIW, what does the ammeter or loadmeter read when this problem occurs? Any rapid oscillations?
Click to expand...

Haven't checked -- will look for this too. I think I need to start digging around behind the panel though, which I haven't done yet because access is a pain.

Thanks everyone!
 
If you can't open breakers manually, maybe pull one radio and see how the other one sounds by itself. Are there any coax connections you can make temp changes to? Maybe pull breakers or fuses to other equipment that could be causing interference.
 
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