I have found one of the most effective tools for tracking down line noise
and electric fence QRM is a little hand-held portable radio from Radio
Shack. It has the AM broadcast band, FM and "aircraft". The aircraft band
is just above the FM BC band, but uses AM. The whip antenna can be
retracted to reduce sensitivity as the noise source is approached. I have
been able to locate noise sources to the exact pole using one of these
things. A AM broadcast receiver is all but useless because at those
frequencies the noise may travel along the lines for miles. Of course, you
want to avoid an aircraft receiver that features a built in noise blanker
that cannot be turned off.
A general coverage receiver works better still. One can get a general
location of the noise starting at the lower frequencies, and keep tuning
higher until the noise is almost gone. Then travel up and down the line
till the noise reappears, follow it to the strongest point, then keep
repeating the process. By the time you get to 10m, you should be pretty
close to the source, The VHF aircraft band radio can be used to pinpoint it
exactly.
One major problem I have lately is that EVERY vehicle we now own puts out so
much ignition garbage that it obliterates all but the strongest line noise
on the portable radio. The required travelling distances are useally too
great to walk, and it is unsafe to attempt to ride a bike along our local
highway because of idiot drivers. Evidently the problemt with the cars is
electronic ignition, since noise tracking was less a problem in older
vehicles that used mechanical ignition points.
Don K4KYV
_________________________________________________________________
Help STOP SPAM with the new MSN 8 and get 2 months FREE*
http://join.msn.com/?page=features/junkmail
|