What's a good method for finding short duration interference?

My 440 repeater is plagued by an interfering signal that lasts a small
fraction of a second, just long enough to bring up the repeater,
and repeats randomly every 20 seconds or so.
Comes and goes...Seems to be dependent on outside temperature.
Sometimes sounds like there's hum on the signal.
First thought was that it was one of those oscillating Winegard
RV TV antennas, but it doesn't seem to drift around like they
typically do.

I hooked the repeater antenna up to the spectrum analyzer,
but the duration is too short to get thru the filters at
the bandwidth required to get any sensitivity.

I can hear it on the mobile.
I've driven around the neighborhood, but the duration is so short
that I've not been able to track it down. Strength seems to peak
at different places blocks apart...but it's hard to tell.

I have some experience with a double duckey and started designing
a doppler system, but it occurs that the short duration signal
will be completely washed out by the Switched Cap Filter. Don't see
how I'm gonna get the low rep-rate signal past the noise. Filter
types that I know about ain't gonna work.

Ideas?
Thanks, mike

mike wrote:

What's a good method for finding short duration interference?

My 440 repeater is plagued by an interfering signal that lasts a small
fraction of a second, just long enough to bring up the repeater,
and repeats randomly every 20 seconds or so.
Comes and goes...Seems to be dependent on outside temperature.
Sometimes sounds like there's hum on the signal.
First thought was that it was one of those oscillating Winegard
RV TV antennas, but it doesn't seem to drift around like they
typically do.

I hooked the repeater antenna up to the spectrum analyzer,
but the duration is too short to get thru the filters at
the bandwidth required to get any sensitivity.

I can hear it on the mobile.
I've driven around the neighborhood, but the duration is so short
that I've not been able to track it down. Strength seems to peak
at different places blocks apart...but it's hard to tell.

I have some experience with a double duckey and started designing
a doppler system, but it occurs that the short duration signal
will be completely washed out by the Switched Cap Filter. Don't see
how I'm gonna get the low rep-rate signal past the noise. Filter
types that I know about ain't gonna work.

Ideas?
Thanks, mike


You need a professional direction finding gear, probably from the DoD
marketplace.

You can by all means build gear to trace this kind of interference but be
adviced! the Guru factor is very high!

If you set up an array of 3 or 4 antennas, you can compare the phase
difference from the different antennas and by that triangulate the
position. You need to have a fast trigger mechanism and memory to be able
to make a constant monitoring with a monitoring stop triggered by your
signal. As a receiver, you should probably use a sdr rig or a wide 1 Msp
ADC to catch spur's on 440.

In other words... It have to be very annoying before one starts of this
expensive hunting of spurs!

A nice project for homebrewing tho'


Cheers

Dan / M0DFI

On Tue, 18 Apr 2006 03:40:12 -0700, mike wrote:

What's a good method for finding short duration interference?

My 440 repeater is plagued by an interfering signal that lasts a small
fraction of a second, just long enough to bring up the repeater,
and repeats randomly every 20 seconds or so.
Comes and goes...Seems to be dependent on outside temperature.
Sometimes sounds like there's hum on the signal.
First thought was that it was one of those oscillating Winegard
RV TV antennas, but it doesn't seem to drift around like they
typically do.

I hooked the repeater antenna up to the spectrum analyzer,
but the duration is too short to get thru the filters at
the bandwidth required to get any sensitivity.

I can hear it on the mobile.
I've driven around the neighborhood, but the duration is so short
that I've not been able to track it down. Strength seems to peak
at different places blocks apart...but it's hard to tell.

I have some experience with a double duckey and started designing
a doppler system, but it occurs that the short duration signal
will be completely washed out by the Switched Cap Filter. Don't see
how I'm gonna get the low rep-rate signal past the noise. Filter
types that I know about ain't gonna work.

Ideas?
Thanks, mike

can you just duck the problem and use a PL tone Iknwo when we lived in
sprinfeild it worked welll a 2 m repeater and another 440repeater in
the general area that worked out well too

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Check this link and see if you have same problem....

www.qsl.net/va3bmc/inter477.pdf

mike wrote:

What's a good method for finding short duration interference?

My 440 repeater is plagued by an interfering signal that lasts a small
fraction of a second, just long enough to bring up the repeater,
and repeats randomly every 20 seconds or so.
Comes and goes...Seems to be dependent on outside temperature.
Sometimes sounds like there's hum on the signal.
First thought was that it was one of those oscillating Winegard
RV TV antennas, but it doesn't seem to drift around like they
typically do.

I hooked the repeater antenna up to the spectrum analyzer,
but the duration is too short to get thru the filters at
the bandwidth required to get any sensitivity.

I can hear it on the mobile.
I've driven around the neighborhood, but the duration is so short
that I've not been able to track it down. Strength seems to peak
at different places blocks apart...but it's hard to tell.

I have some experience with a double duckey and started designing
a doppler system, but it occurs that the short duration signal
will be completely washed out by the Switched Cap Filter. Don't see
how I'm gonna get the low rep-rate signal past the noise. Filter
types that I know about ain't gonna work.

Ideas?
Thanks, mike


--
Joe Leikhim K4SAT
"The RFI-EMI-GUY"©

"Treason doth never prosper: what's the reason?
For if it prosper, none dare call it treason."

"Follow The Money" ;-P