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Author Topic: Unidentified signal on 4125, 6215, 8414, 12290, 12577 and 13500 kHz  (Read 6775 times)

Offline SW Observer

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Unknown noise/mode, broadcasting presently on ALL frequencies simultaneously in H3E.

Station was heard best in New York on 12290 and 13500 kHz but also audible on 6215 kHz and 8414 kHz.

Signals have been strongest in Europe and are being monitored via the WebSDR, I have provided a recording of the transmission, if anyone can identify this broadcast or shed some light on it, that would be greatly appreciated!!!


All the best,

RW Observer
« Last Edit: June 29, 2015, 0128 UTC by RW Observer »
Florida, always listening via my Tecsun PL-660 receiver.

Offline osiris

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Here's some info I found.

* XIEGU X6100 - MLA-30 Loop
* Eton Elite 750 - MLA-30 Loop
* AirSpy HF - qQRX - MLA-30 Loop

Loc: North-Central, PA - FN11

I gladly accept QSLs. Please eMail to: teslaintheaether@gmx.com

Offline Token

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This signal, or one very much like it, has been seen periodically for years on HF.  As far as I can tell it was first documented in 2011 when it intruded on a ham band (40 meters), but I believe it was around before then, at least I have some entries in my log that are probably it before then.  It was suggested, at least presented as a question, in “Radar Systems on Shortwave” by DK2OM, as a possible radar, but I find this extremely unlikely for a variety of reasons.

At least one version has been DFed to the region around Israel.

Lets start with the basics of what it is as a signal.  There is some variability in the signals as seen, but you can narrow the description down a bit.  So my description will be as the signal has appeared most times in my log book, and may not represent the only possible conditions.

Typically the mode of operation is J3E (single sideband suppressed carrier), H3E (single sideband reduced carrier), or R3E (single sideband full carrier).  I have seen H3E or R3E most often, and the single sideband used is most often USB.  Sometimes the other sideband well suppressed, sometimes it is poorly suppressed, and sometimes it is almost as strong as the primary sideband.  So it looks to me most often as if it intends to be H3E USB, although R3E and full DSB AM are also common.

As near as I can tell, the frequency range reported has been everything from about 4 MHz to about 17 MHz.

The audio is most often a triangle wave sweeping from about 0 Hz to about 5 kHz.  The upper frequency limit is typically not seen, as it appears the audio passband of the transmitter cuts off at about 4 kHz.  However if you plot the sweeps, both up and down, it is often clear that they intersect at about the 5 kHz point.

When the “other” sideband is poorly suppressed, or not suppressed at all, this can lead to what looks like an “X” pattern on the waterfall, with the carrier as a line down the center of the X.

There appears to be some instance to instance variability in the sweep cycle time, but I have seen it most often at about 6 seconds per cycle.  The cycle time is generally stable within a given transmission period.  By that I mean the cycle time can be different during different transmissions (different days for example), but does not appear to drift during any given transmission.

Harmonics of the audio are often present.  Most often at least the 2nd harmonic is seen, and when the signal is strong it is not unusual to see the 3rd to 5th harmonic.  Since the harmonics must have a faster chirp rate and visual slope on a waterfall, this leads to multiple triangles all coming to the same apex at the same time, each harmonic with a more acute included angel than the last.  The audio interaction of these harmonics can make for interesting affects in the ear.

So, what is it?  As far as I know no one has presented any suggestion as more than a possibility.  I will say, I have used audio test signals essentially identical to this to test gear before.  And until some compelling data comes forward to suggest otherwise that is my bet, this is some kind of test signal, an audio test tone injected into the modulation chain at some point to test either the audio feeding a transmitter, or to test the transmitter itself.

Hey, it is not as sexy an answer as “spook signal to covertly transfer encrypted data”, but it seems the most likely answer to me.

« Last Edit: June 30, 2015, 2144 UTC by Token »
Mojave Desert, California USA


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