"Steve Nosko" wrote in message
...
Actually, if there is an *easy* way, I'd sure like to know!

I started my DF'ing in the Navy in the late 60's, so I'm no slouch.
This is a very sticky problem; few ways to do this. All phase systems
(Doppler, TDOA) require the signal to be well centered in the IF and a
well
behaved IF to boot. The amplitude systems (beam, single / dual cardioid)
are better for this, but the sweep-width of this signal makes the beam
less
effective due to the change in gain as you get off the design freq.

If I had the time, I'd modify a wide band FM receiver (like a broadcast
receiver 88-108) with a *really* aggressive AFC so it would follow the
bogie
along. Then a TDOA should work. Actually any would be better with this
receiver, but I would have to do a little characterization across the
expected freq range first.

I think *any antenna* and a spectrum analyzer watching signal strength is
the best bet...already done some of that. The biggest problem is that it
is most active when we have the least time to hunt.
Steve





"Crazy George" wrote in message
...
Ed:

I think Steve would be interested in hearing a methodology for DFing a
non-stationary signal, as would I. I have tried to track one of these
spurs
with a receiver while simultaneously attempting to get a bearing, and
gave
up. The Doppler DF systems need it in the passband and frequency stable
for
at least one "revolution" of the virtual antenna, which doesn't happen,
so
let's hear what works.

--
Crazy George


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

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

"Gary Schafer" wrote in message
...
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


OK. Got it. Remember to not eliminate Tx spur / IM. We had one spur
occurrence last year and the two repeaters were 20 miles apart...but it was
a pretty bit Tx spur. Interesting how this PA spur just landed on the other
repeater input so nicely.
Steve

"Steve Nosko" wrote in message
...

"Gary Schafer" wrote in message
...
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


OK. Got it. Remember to not eliminate Tx spur / IM. We had one spur
occurrence last year and the two repeaters were 20 miles apart...but it
was
a pretty bit Tx spur. Interesting how this PA spur just landed on the
other
repeater input so nicely.
Steve



If it had landed on some other frequency, you would never have noticed it.
The odds of it affecting you were really quite low, despite Murphy's Law.
And logically, there's nearly an infinite number of other problems that
could happen, given just the right tweak or failure someplace.

Ed
wb6wsn

Bottom post:
"Ed Price" wrote in message
newsN0Zb.3320$C21.1209@fed1read07...

"Steve Nosko" wrote in message
...

"Gary Schafer" wrote in message
...
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


OK. Got it. Remember to not eliminate Tx spur / IM. We had one spur
occurrence last year and the two repeaters were 20 miles apart...but it
was
a pretty bit Tx spur. Interesting how this PA spur just landed on the
other
repeater input so nicely.
Steve



If it had landed on some other frequency, you would never have noticed it.
The odds of it affecting you were really quite low, despite Murphy's Law.
And logically, there's nearly an infinite number of other problems that
could happen, given just the right tweak or failure someplace.

Ed
wb6wsn


Yea. sorta' except that it sweeps through repeater outputs and other
inputs, just not coming to rest on them, ever.

Weird.
P.S. Did you know that Murphy's law was discovered by a *DIFFERENT* Murhy?