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Single COM Frequency Interference

macrafic

Well Known Member
I have a weird problem in my RV-7A.

When I dial in 119.8, which happens to be Approach/Departure frequency for KRST (Rochester, MN), and my LED NAV lights are on, I get a steady squelch on/squelch off sound, steadily about once every 1-2 seconds. When the sound comes on, the RX indicates on the GTN 650. The same thing happens with my 2nd radio. When I am actually receiving or transmitting to ATC, this behavior stops, but starts again as soon as there is no transmitting. If I turn my NAV lights off, it goes away.

It would be easy to blame some crossover of energy between the wiring for the lights and the COM antennas, but here is the kicker. 119.8 is the ONLY frequency where this occurs!!!

Not sure how to start debugging this. It would not be such a big deal, except KRST is my home airport and I use this frequency a LOT!

Any of you COM/Radio gurus out there have any ideas?
 
Your nav lights are probably producing a harmonic of that frequency. Knowing what type of lights they are might help. Shielding of the power wires and proper grounding are essential.
 
Noise

I had a similar problem with my LED landing lights. When I used the wigwag or switched them on I would have the symptoms you describe on 2 different frequencies. Our electronics guru made me some filters which helped but did not eliminate the issue. I tested another manufacturer of LEDs with the filters and the problem was gone. If I was doing it again I would have just used aviation products which are noise free, instead of going through the hassle. My Aveo LED nav/strobe lights were never an issue.

Al
 
Your nav lights are probably producing a harmonic of that frequency. Knowing what type of lights they are might help. Shielding of the power wires and proper grounding are essential.

My tail NAV is an AeroLED light, and I took pains to make sure it was grounded and shielded properly, per the instructions, since my Garmin G3X is back there also.

My wingtip NAVs are CreativAir (KillaCycle) lights.

One thing I can do is disconnect each, one at a time, and see which one might be causing the issue. Just tough to do that with our cold weather here in Minnesota and no heated hangar. May have to wait a while.
 
There is a known issue with a generation of AeroLEDs from 2016 known to cause interference, I would start there since it sounds like what you are describing. I'm sketchy on the details but they replaced mine which were shipped from Van's warehouse (older stock) with newer units marked specifically as "12V".
 
you can try to purchase different capacitors values
and try them a cross power feed to LEDs if you have oscilloscope and someone who knows how to use it
that would help a lot to narrow down harmonics you trying to filter out
 
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