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Strange Noise on my Comm's

L

lr172

Well Known Member
Somewhere in the last couple of months, my Comm radios have developed an annoying problem. I cannot pinpoint exactly when this behavior began, but it is on the recent past and I haven't added too much equipment recently.

I am occasionally receiving a very load sound on the comms. It is hard to describe, but like a squealing, but deeper toned. The sound is very stable in nature, with no oscillation or on/off component like static. It sounds like an electronic noise. It comes in quite a bit louder than the voices that the Comm picks up at any given volume setting. It typically lasts for 10 seconds, but can be longer or shorter. Occasionally it will start and stop a few times. I more commonly pick it up on my KY96 radio, but sometimes get it on the 430W.

The interesting part is that it only happens when 1500' AGL or lower and only when near airports with an ILS. It is more common lower and often happens in the flare or short final. It first happened in the flare and scared the **** out of me.

I am a bit stumped. At first I thought it was some electrical interference in the panel, but don't see how that fits with the limited geography of the occurrences. I thought wiring or antenna, but it is happening to both radios (separate wiring runs and antennas).

I would appreciate any help from the RF experts, as well as others that have seen similar issues.

Thanks,

Larry
 
This is merely the sound Lifties make when the plane gets close to the ground and they start getting excited. Lifties are microscopic creatures that are responsible for our wings being able to support the weight of the plane and occupants. At least that is the way it was described to me. If the sound does start oscillating it is usually due to a PIO and angry Lifties. I've heard them getting agitated during the few times I've attempted to "jack up the runway" during gusty conditions.
 
I've had the same experience, at least 3 times, and until your post, Larry, I thought it was my leg hitting/rubbing the jack/plug connection on my subpanel (on a C172). It only happens to me during the flare. Interesting. Definitely some kind of gremlin, but I thought it was electrical rather than RF energy. And yes, it happens on a runway that has an ILS, and when I'm landing counter to the ILS landing direction. Somehow I don't think it's aerodynamic energy. Sorry, Sam. ;-)
 
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rv7boy said:
And yes, it happens on a runway that has an ILS, and when I'm landing counter to the ILS landing direction. ;-)
Click to expand...

Does it sound like 90 and/or 150 Hz? If so you?re somehow picking up the localizer (the localizer is physically at the end of the runway opposite the approach end).
 
BobTurner said:
Does it sound like 90 and/or 150 Hz? If so you’re somehow picking up the localizer (the localizer is physically at the end of the runway opposite the approach end).
Click to expand...

I am not really sure what 90 or 150 hz sounds like, but I know that is low on the spectrum. The noise is clearly low pitched. While it typically happens within a mile of the field, I was getting it yesterday over 5 miles away while shooting approaches in light rain. That one was just before intercepting the localizer.

The real question is why am I picking up the localizer on my com radio. Unlike Sam, I sometimes get this a good ways before the flare. In yesterdays event while joining the localizer, I switched radios and the other wasn't experiencing it. I assumed the reception at the longer distance yesterday was somehow related to all of the moisture in the air (1 mile visibility with light rain). I previously never got it that far before.

Larry
 
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BobTurner said:
Does it sound like 90 and/or 150 Hz? If so you’re somehow picking up the localizer (the localizer is physically at the end of the runway opposite the approach end).
Click to expand...

I also cannot say from memory whether it was 90 or 150 Hz. But it only happened to me when I was within 5 feet (apx.) of the runway and going counter to the ILS direction. I can't say for sure if either of my nav radios was tuned to the ILS frequency, but the next time I land I'll try to duplicate it. When it happened I just wrote it off as old avionics connections. It's an old 172.
 
Talked to a designer at Bendix King. He had a very difficult time believing that I was picking up a localizer on the radio. A strong FM station was more believable to him.

What I learned was that several older ELTs had a reputation for re-radiating strong signals at times. What they re-radiate is very broad in bandwidth and can impact Comm frequencies. He said that the localizer signal is not strong enough to cause re-re-radiation. It is usually things like FM transmitting stations. Given this always happens in the airport environment, I am thinking that there is something else at these larger, ILS airports that have strong RF transmissions.

Either way, the recommendation was to disconnect the ELT antenna and see if the problem disappears. Interestingly, while researching this issue on the web I found a similar type of problem and a wise old tech recommended disconnecting the ELT antenna and the problem was solved.

I am hopeful this will address the issue and will report my final results on this thread.

Larry
 
sound

Maybe something is going to ground my plane was parked overnight in a rain storm a couple weeks ago and when I used radio got a loud sound in transmit lucky it quit when it dried out.
Bob
 
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