Need help identifying jammer signal

GNU Radio
1

Hi,

In the last few days a signal has entered in the center of our
incoherent
scatter radar band. It drifts between 440.1 and 440.4 MHz very slowly
and
has approximately a 10 kHz bandwidth. A scope plot of the signal shows
something that looks a little bit like frequency shift keying. While the
frequency is stable on short time scales, the signal tends to drift a
lot
on the scale of days, suggesting that whatever is causing this signal,
it
is broken.

I’ve attached a GRC plot of the signal. In the plot, the jammer is at a
+166 kHz offset. The scope plot is centered at this frequency and has a
40
kHz bandwidth.

Does anyone have any idea what this could be?

juha

2

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3

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4

On 12/06/2013 02:12 PM, Johnathan C. wrote:

If you want, I could let you upload a capture file to gnuradio.org so
everyone could join the hunt.
The hunt for RFI October.

“This signal will get worse. It’ll get worse, and we’ll be lucky to
live through it.”

5

Hi guys,

Thank you for your helpful suggestions. We still haven’t managed to
pinpoint where the signal is coming from, but we have just dispatched a
black SUV with a three letter acronym stencilled on it (our university’s
initials) to hunt for the signal with a spectrum analyzer and a yagi.

Yesterday the interference was a 440.4 MHz and during the night it went
down to 440.0 MHz. Today it has drifted up and down between 440.0 and
440.2
MHz. This is very annoying as our frequency is 440.2 MHz. Based in the
wild
fluctuation in center frequency (including > 20 kHz jumps), However, the
signal at close inspection kind of looks like FSK, so maybe whatever it
is,
isn’t working properly anymore.

I recorded a 10 second snippet of 50 kHz baseband signal in interleaved
I
and Q with 32-bit floating point format. In python, one would read this
with this command:

import numpy
z = numpy.fromfile(“rfi.bin”,dtype=numpy.complex64)

The file can be downloaded here:

http://www.haystack.mit.edu/~j/rfi.bin

You can probably feed this into gnuradio with the filesource and complex
data type.

Patrik, you are doing cool stuff with the POES satellite receiving. I
wish
I had time to try that at some point.

juha

6

Terve Juha,

Some animal neck collar TX:er are very close to that feq (440 MHz).
It could be on a wolf, reindeer or a hunter that use a home brew
(illegal) collar on his dog. Building a home brew dog collar is
popular today since you can get parts without any questions asked…

I would contact the person who count wolfs near you.

Eagles here (Vaasa, FI) use ARGOS up-link to POES sats 401.65 and
downlink 465.98 MHz (bw 24/80/110 kHz).

Patrik

7

In Germany such signals often came from oscillating TV antenna preamps,
long forgotten and out of use on top of a roof, but still
powered.usually the BNetzA (the regulation authority) was very helpful
in finding those.

Ralph.

From: discuss-gnuradio-bounces+ralph=removed_email_address@domain.invalid
[mailto:discuss-gnuradio-bounces+ralph=removed_email_address@domain.invalid] On Behalf Of
Juha V.
Sent: Tuesday, 10 December, 2013 04:26
To: Patrik T.
Cc: gnuradio mailing list
Subject: Re: [Discuss-gnuradio] Need help identifying jammer signal

Hi guys,

Thank you for your helpful suggestions. We still haven’t managed to
pinpoint where the signal is coming from, but we have just dispatched a
black SUV with a three letter acronym stencilled on it (our university’s
initials) to hunt for the signal with a spectrum analyzer and a yagi.

Yesterday the interference was a 440.4 MHz and during the night it went
down to 440.0 MHz. Today it has drifted up and down between 440.0 and
440.2 MHz. This is very annoying as our frequency is 440.2 MHz. Based in
the wild fluctuation in center frequency (including > 20 kHz jumps),
However, the signal at close inspection kind of looks like FSK, so maybe
whatever it is, isn’t working properly anymore.

I recorded a 10 second snippet of 50 kHz baseband signal in interleaved
I and Q with 32-bit floating point format. In python, one would read
this with this command:

import numpy

z = numpy.fromfile(“rfi.bin”,dtype=numpy.complex64)

The file can be downloaded here:

http://www.haystack.mit.edu/~j/rfi.bin

You can probably feed this into gnuradio with the filesource and complex
data type.

Patrik, you are doing cool stuff with the POES satellite receiving. I
wish I had time to try that at some point.

juha

On Sun, Dec 8, 2013 at 5:38 AM, Patrik T. [email protected]
wrote:

Terve Juha,

Some animal neck collar TX:er are very close to that feq (440 MHz).
It could be on a wolf, reindeer or a hunter that use a home brew
(illegal) collar on his dog. Building a home brew dog collar is
popular today since you can get parts without any questions asked…

I would contact the person who count wolfs near you.

Eagles here (Vaasa, FI) use ARGOS up-link to POES sats 401.65 and
downlink 465.98 MHz (bw 24/80/110 kHz).

Patrik

On Fri, 2013-12-06 at 13:48 -0500, Juha V. wrote:

I’ve attached a GRC plot of the signal. In the plot, the jammer is at
a +166 kHz offset. The scope plot is centered at this frequency and
has a 40 kHz bandwidth.

Does anyone have any idea what this could be?

juha

8

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9

These look like 2pi jumps – which is the an artifact if the unwrapping
is not working well.

10

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11

Last Friday we managed to finally track this thing down. It was a broken
FSK telemetry system on an FM radio tower. It was about 30 km Southwest
of
our radar.

I did a small write up about this:

Thanks for all the help.

juha

On Wed, Dec 11, 2013 at 4:34 PM, Johnathan C.

12

Thanks for the follow-up, this is similar to a 1 second noise burst
every 60
seconds or so we had on our ham repeater. The reason could be identified
after months of search by coincidence. The repeater sysop visited his
fathers office, monitored the input frequency of the repeater like he
had
done routinely for months to hear exactly nothing - but there it was,
some
wideband noise pulse! 100 m from this office a paging system for a
facility
management team was sitting on a tower, not actively used for years,
still
transmitting its beacon every minute, and with age the TX started
emitting
noise along with its POCSAG signal. Gnuradio also would have been useful
in
our case, but it was way before we knew of this exciting stuff :slight_smile:

Ralph.

From: discuss-gnuradio-bounces+ralph=removed_email_address@domain.invalid
[mailto:discuss-gnuradio-bounces+ralph=removed_email_address@domain.invalid] On Behalf Of
Juha
Vierinen
Sent: Tuesday, December 17, 2013 11:41 PM
Cc: gnuradio mailing list
Subject: Re: [Discuss-gnuradio] Need help identifying jammer signal

Last Friday we managed to finally track this thing down. It was a broken
FSK
telemetry system on an FM radio tower. It was about 30 km Southwest of
our
radar.

I did a small write up about this:

Thanks for all the help.

juha

On Wed, Dec 11, 2013 at 4:34 PM, Johnathan C.
[email protected]
wrote:

On 12/10/2013 02:00 PM, Miki Lustig - KK6GEO wrote:

These look like 2pi jumps – which is the an artifact if the
unwrapping is not working well.

Sure, I see what you mean.

Backing up and just plotting the unwrapped phase, you can see in the
first image that overall it is increasing at one rate, then shifts to a
lower rate about 1.5 seconds into the file.

The finer structure is much more interesting. The second image shows
the phase making fast jumps every 500 samples (10 ms), with periods of
oscillation in between. The detail on this is in image 3.

I still have no idea what this is, but it sort of looks like an
oscillator that is disciplined at 100 Hz.

13

Well done!

Patrik