On Wed, 18 Feb 2004 03:17:37 -0800, "Ed Price"
wrote:



I agree with Steve's observations (although I prefer that he bottom-post),
but I would still try to keep the process simple.

First, you know the very limited frequency range of the offending signal
(you said it slowly drifts across your repeater input at 145.41 MHz). So
that means you know which way it drifts, about how fast the frequency slew
is, and about how far it shifts. Further, you know the characteristic
modulation on the signal. And, to make it even easier, the signal isn't
playing tricks on you to spoof your search. Finally, you must have some idea
by now as to when the signal is most likely to be present.

Time to get a directional antenna (Yagi, log periodic, a loop resonant to
145 MHz, even an inefficient horn) and look for the signal. I would use a
spectrum analyzer (those HP boxes are too big and heavy, so look for a
Leader or Anritsu. Why not turn this into a real learning experience? Why
not build a 2 meter version of the Poor Man's Spectrum Analyzer into a
briefcase, maybe updating the display by using a small laptop?

As a first assumption, I suppose we can assume that the offending signal
isn't in a vehicle. So get out and grab a bearing when you can. Obviously,
you have to be prepared to get into the field quickly and efficiently to
make your observations. After a couple of bearings, at least you will guess
which side of town to look first.

Hey, if this was easy, then T-hunts would be no fun, and clandestine radio
would be a short path to a bullet.

Ed
wb6wsn

It sounds a lot easier than it is. Sometimes the interference that you
hear is the result of a spur from one transmitter getting into another
and the IM product of the second is what you hear. Try and track that
one down!
The most successful way I have seen is to first find the general
direction the problem is coming from (spectrum analyzer and
directional antenna) and then spending many hours watching the
spectrum analyzer to see what transmitters come on the air when the
interference is present.

Problem is that they are not always there. Temperature difference at a
particular site can cause the spur to change or not be there. Amount
of use of the transmitter can make a difference. These things can
drift across the whole VHF band or more.
73
Gary K4FMX