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Author Topic: Any ideas what this could have been?  (Read 3810 times)

Offline jFarley

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Any ideas what this could have been?
« on: August 23, 2012, 0053 UTC »
I had the rx capturing on 6925 USB while I was doing other stuff, when I heard a couple of tones in the passband.  Looked up to see an brilliant AM carrier on 6970 with very wide (lower at least) sidebands.  I estimate from the color palette that this was at least -50dBm, and add another 10dB as I was not tuned to 6970.  It seemed to be there only 5 to 10 seconds.  I did not react fast enough to cap a screen while the signal was still up in the FFT, but the waterfall had not refreshed yet.



Any one else cap this?
« Last Edit: August 23, 2012, 0211 UTC by jFarley »
Joe Farley, Near Chicago
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cmradio

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Re: Any ideas what this could have been?
« Reply #1 on: August 23, 2012, 0617 UTC »
OTH radar?

Peace!

Offline ChrisSmolinski

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Re: Any ideas what this could have been?
« Reply #2 on: August 23, 2012, 1256 UTC »
Yes, I recorded it as well, here's the spectrum and waterfall during the transmission:


Chris Smolinski
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Offline jFarley

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Re: Any ideas what this could have been?
« Reply #3 on: October 02, 2012, 0042 UTC »
Noted again today for a few seconds at 2221.  Similar spectrum as Chris posted above.  Around S9+10 here for the 6970 peak.
Joe Farley, Near Chicago
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Offline jFarley

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Re: Any ideas what this could have been?
« Reply #4 on: December 12, 2012, 2312 UTC »
12Dec12

Just noted this again at 2309 today.  On for a few seconds.
Joe Farley, Near Chicago
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Offline Token

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Re: Any ideas what this could have been?
« Reply #5 on: December 13, 2012, 1838 UTC »
I missed this posting when it was first up in August.

This is a signal I have been seeing and paying attention to for 6 or 8 months.  I see it very seldom, I mostly only see it during the week, and I mostly only see it during what would be considered the work day in North America.

6970 kHz is just one of the frequencies it hits.  Most commonly I see it start low (say around 4 MHz) and work its way up in freq, spending anything from a few seconds to several minutes on each freq.  I have seen it go as high as 28 MHz.

The transmissions are not all the same, but follow a few basic formats, with variations.

Often it starts with a simple carrier, sometimes there are amplitude variations on the carrier that look like a signal being peaked or tuned.  Sometimes a very shallow AM modulation follows the carrier, say 4.2 kHz and 10% or less modulation depth.  It typically goes to the pulsed signal just before it leaves a specific frequency.  The time it is in this pulsed mode can be very short, several seconds, to several minutes.

During the pulsed portion of the signal the pulse duration is generally around 830 microseconds in length and the PRF (pulse repetition frequency) is generally about 303 Hz.  Because of these numbers, particularly the pulse width, it is unlikely to be a radar of any kind.

Such a pulse width would give a range resolution of about 125 km (since there does not appear to be any pulse compression), or two targets would have to be 125 km apart before they could be distinguished as two targets, and not just one.  While the maximum range that PRF allows (since there does not appear to be any pulse coding) is about 495 km.  So, if this were a radar it would be one that could only see 495 km, but not tell two targets 120 km apart from each other.  Not very likely.

It just so happens I have several pictures and a video online of the signal on 6970 kHz, and just a week or so before your report.  I have other frequency SDR recordings and pictures, but the 6970 kHz is the ones I put online.

Video here:
http://www.youtube.com/watch?v=3AIZLc-ZqW0

Image here, annotated to show the spectrum of the pulsed transmission.  The spectral purity is pretty good indicating a pulse with a good rise and fall time.


Unannotated image here:



I have not seen this signal in a couple of months, and I look for it regularly.  Tomorrow (today is my Friday, so the start of my weekend is tomorrow) I will have to look for it again.

T!
T!
Mojave Desert, California USA

cmradio

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Re: Any ideas what this could have been?
« Reply #6 on: December 13, 2012, 2030 UTC »
Data.

Has anybody tried to decode it? ???

Peace!

Offline Token

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Re: Any ideas what this could have been?
« Reply #7 on: December 13, 2012, 2202 UTC »
Data.

Has anybody tried to decode it? ???

Peace!

The pulsed section is not data that I can detect.  It is a simple pulse that is about 830 microseconds long and happens about 303 times per second.  There is no modulation on the pulse and the pulse does not vary in any significant way from start to finish.

Of course, I guess it could be viewed as data…but if so all the information is the static, always ones or zeros ;)

T!
T!
Mojave Desert, California USA

Offline jFarley

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Re: Any ideas what this could have been?
« Reply #8 on: December 13, 2012, 2251 UTC »
I've seen this now 3 or 4 times, all near 6970.  I was not aware of operation on other frequencies, so I appreciate hearing about that.  The TXs I have seen have all been relatively short, 5-10 seconds, and have generally caught me by surprise.  IIRC, at least one of these had a few seconds of carrier alone before modulation started.

Thanks guys for your comments on possible purpose for this; I am not qualified to speak on that.
Joe Farley, Near Chicago
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Offline Token

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Re: Any ideas what this could have been?
« Reply #9 on: December 14, 2012, 0118 UTC »
Was at work when I posted the earlier comments, now am at home and can check the logs.

Looking back through the logbook I see I first received this signal in early April, 2012.  I got it again in May, August, and September.  In the log I show the frequencies as 5385, 6970, 7595, 7990, 9050, 9803, 11064, 16060, 17048, 18036, 19270, 21460, 23180, 24450, and 26875 kHz (and log shows I have at least one I/Q file from each of those freqs).  It appears to use the same frequencies each time I see it, I mean in May, August, and September I saw many of the same freqs.  I have a note in my log that “saw frequencies just above 4 MHz on wideband display but never got center freq”.

ChrsiSmol, note that 9050 kHz.  Might not mean anything but I think your ditters hit that freq and I know the shorter ditters from April did.

T!
« Last Edit: December 14, 2012, 0121 UTC by Token »
T!
Mojave Desert, California USA

Offline ChrisSmolinski

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Re: Any ideas what this could have been?
« Reply #10 on: December 14, 2012, 1102 UTC »
Yes Token, 9050 was used by the ditters.
Chris Smolinski
Westminster, MD
eQSLs appreciated! csmolinski@blackcatsystems.com
netSDR / AFE822x / AirSpy HF+ / KiwiSDR / 900 ft Horz skyloop / 500 ft NE beverage / 250 ft V Beam / 58 ft T2FD / 120 ft T2FD / 400 ft south beverage / 43m, 20m, 10m  dipoles / Crossed Parallel Loop / Discone in a tree

Offline jFarley

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Re: Any ideas what this could have been?
« Reply #11 on: December 14, 2012, 1426 UTC »
Noted this guy again last night (14Dec12) on 6970 at 0155.  Much weaker than normal level.
Joe Farley, Near Chicago
SDR-IQ / R8 / R7
Remote Resonant Loops for HF and LF / ALA 1530
Active 60" Whip / PA0RDT
QSLS appreciated to:    jfarley44@att.net

 


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