rb wrote:

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.

Your transmitter may have an intermediate beat frequency of about 21.7
Mhz. This would explain the aircraft interference. 104.1 + 21.7 =
125.7. The aircraft you hear are most likely broadcasting somewhere
around 125.7 Mhz (which is in the middle of the air band), 125.7, 125.75,
126 Mhz, etc. Filtering out such images can be difficult. Your
electronics are unfortunately probably not very good at filtering this
out. Also, aircraft radios use AM, and your FM equipment should have a
filter to effectively remove AM signals, but apparently it is not doing
this well.

Are you fairly close to an airport that Southwest lands at? Your house is
probably under a sector that uses a frequency that your equipment is
sensitive to. It could be high altitude communications, although if you
are near an airport the aircraft would be closer and have a stronger
signal for you so I think that is more likely. (Aircraft radios only
transmit with a few watts, compared to maybe 50,000 watts for an FM
broadcast station. You are probably receiving broadcasts from the air,
unless you are very close to a ground transmitter station.

I have experienced this myself with just a cheap FM radio. Aircraft
frequency 118.5, radio station 96.9. Aircraft communications were not
very clear, but it was obvious what it was when planes were very close.