---------------------------------------------------------- Avionics-List Digest Archive --- Total Messages Posted Sat 09/03/11: 3 ---------------------------------------------------------- Today's Message Index: ---------------------- 1. 09:32 AM - Hum in Radio? (Goodone) 2. 01:23 PM - Re: Hum in Radio? (Doug McNutt) 3. 05:18 PM - Re: Hum in Radio? (Goodone) ________________________________ Message 1 _____________________________________ Time: 09:32:35 AM PST US Subject: Avionics-List: Hum in Radio? From: "Goodone" I have an Icom IC-A24 Aviation Transceiver mounted in my aircraft with an external antenna. The radio sends and receives while in the air very well. However, when I am on the ground at airports with a control tower or Unicom I get a hum in the radio. This also occurs when I am on the ground near another aircraft that has its radio on the same frequency. Where is this hum coming from? I assume that it is some type of feedback but I do not know what to do. Suggestions? Read this topic online here: http://forums.matronics.com/viewtopic.php?p=351323#351323 ________________________________ Message 2 _____________________________________ Time: 01:23:48 PM PST US From: Doug McNutt Subject: Re: Avionics-List: Hum in Radio? At 09:27 -0700 9/3/11, Goodone wrote: > >I have an Icom IC-A24 Aviation Transceiver mounted in my aircraft with an external antenna. The radio sends and receives while in the air very well. However, when I am on the ground at airports with a control tower or Unicom I get a hum in the radio. This also occurs when I am on the ground near another aircraft that has its radio on the same frequency. Where is this hum coming from? I assume that it is some type of feedback but I do not know what to do. Suggestions? Some things to check: Most non-engineers describe "hum" as a low frequency audio noise that is an octave of so lower than middle C. It is usually 60 Hz or 120 Hz noise that comes from a commercial power source. That would be very unusual in a light airplane. But at an airport with big mercury lights, perhaps. If what you hear is a higher frequency it could be originating in your generator or alternator. The test is to move the throttle and report that the tone of the noise changes. Alternators run about 400 Hz which would sound like an A. It's possible for a nearby aircraft to be transmitting because of leakage in the local oscillator of it's receiver. That kind of thing is pretty rare unless the radio has been subjected to unprofessional servicing. You would notice it and remember the aircraft involved. Or do you mean that that other aircraft is deliberately transmitting? I have seen cases in which the aircraft antenna is broken and works only when forward airspeed makes it bend and effectively connect the fine copper tape inside of the fiberglass tube that is the antenna. I don't see how that would generate "hum" though. Perhaps noise because of some automatic gain control though, In short, you need to be more explicit about your problem. -- --> From the U S of A, the only socialist country that refuses to admit it. <-- ________________________________ Message 3 _____________________________________ Time: 05:18:16 PM PST US Subject: Avionics-List: Re: Hum in Radio? From: "Goodone" I would say that the "hum" that I am hearing is about one octave below middle C. It sounds a lot like the noise that you hear when folks are having trouble with feedback with a microphone in a nightclub. I doubt very much that it is from some noise source on the ground. Maybe it is being generated from something in my aircraft that I do not hear while in the air. I also don't think that it is from a bad connection in my antenna since I do not hear it at all on the ground when I am on the grass strip that I operate from. 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