"rb" wrote in message
ups.com...
I bought a FM wireless transmitter to rebroadcast stuff from my PC
around the house. The only frequency I could find was 104.1 that was
clear without a station. But all of a sudden, now when I am
broadcasting my stuff, I pick up planes instead. How can this be? I
know it is from planes, as I hear words like "Southwest", etc. Without
my transmitter on, all I hear is static on 104.1
but when I turn on my transmitter, the planes seem to over ride my
signal.

I can't speak for your specific situation. But generally, you've got a
couple of things going on: frequency harmonics mean that you can get signal
on different frequencies from that actually used by airplanes, and the fact
that airplane radios use AM mean that you don't need to even be on a
harmonic frequency (the AM radio station next to our house produces audible,
intelligible signals on practically any electronic device that has
amplification).

I discovered, once I started using an FM transmitter with my MP3 player in
the car, that once my FM transmitter is turned off, the car radio will pick
up the ATIS broadcast on the frequency I'm using for the FM transmitter
(107.3...but I doubt it matters much).

That said, I would be surprised if you are picking up transmissions from
airplanes themselves. I wouldn't expect their transmitters to be powerful
enough, nor close enough to you to produce a signal you can hear on your FM
receiver. It seems more likely to me that you are near a ground-based
station, with its relatively higher transmitting power, and are hearing that
side of the conversation.

The fact that it occurs only when your transmitter is actually turned on
suggests to me that the interference is actually in the transmitter itself,
especially if you see the same behavior in all of your receivers. Probably
there's some amplifier circuit somewhere in the transmitter that is picking
up the interference, which is then transmitted normally to each receiver.
Why this would override your intended signal in the transmitter, I don't
know...seems like it should be in addition to, rather than instead of (at
least that's been my experience with the interference from our neighbor's AM
radio station). But as I've also found with our various interference
issues, the exact manifestation of the interference can vary widely from
device to device (another reason that, if you are seeing the same behavior
in a variety of receivers, the interference is more likely affecting the
transmitter, since otherwise I wouldn't expect every receiver to be
interfered with in exactly the same way, assuming they aren't all of exactly
the same design).

We do have a couple of people who read this newsgroup who are very
experienced electronics engineers and who may be able to offer more specific
advice once they've read your post. However, you are not actually dealing
with an aviation issue here...you're actually asking about a radio
electronics issue, and as such you are likely to get better information from
a newsgroup dedicated to that topic, rather than aviation.

The one piece of information that you can get here that may be useful is the
range of aviation frequencies: they are from 118Mhz to 136Mhz (there are
navigation radios, on which some voice communications can occasionally
occur, from 108Mhz to 118Mhz, but I doubt these are what you're dealing
with), and as I mentioned before they use AM for the signal.

Hope that helps.

Pete