4200, 4600, 5200 kHz UNID OTHR?

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brandon

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I have seen this last month and I totally forgot about it until tonight after spotting it again. I first noticed it on 4200, then shifted to 4600 and 5200 for about a minute each. Signal was pretty strong at times, so I suspect it might be coming from the west coast.

Here is a recording of it on 5200 kHz mixed with a CODAR as well.
Rec-5.2MHz_14-08-12_02'47'30.wav

Anyone else log this?
 

Token

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Brandon,

What was the width of this transmission? I had originally written a different response here, but re-listening to the recorrding I do not think what you have is the same thing I was responding with. Instead it might be another signal I have been watching for the last year+.

T!
 

brandon

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Hey T. I would say about 20 kHz wide, but I'll have to see it again to confirm.
 

Token

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Yeah, I saw that one active tonight. I have been watching that radar / sounder for close to a year now, trying to figure out where and who.

Because of when I see it, and who else sees it, I suspect eastern side of the Pacific, not yet ruled out South America.

Because of how infrequent it sounds, often much more than 30 minutes between activity, I suspect a sounder or atmospheric radar of some kind, not one meant to track man made objects.

It sometimes uses an interesting waveform. It is LFMCW (Linear Frequency Modulated CW) however using a triangle wave modulation. Most HF radars, almost all others in recent years, use a sawtooth wave when they are LFMCW. The one notable oddball is the new Russian 29B6 Container radar. It uses LFMOP (Linear Frequency Modulation On Pulse), essentially a sawtooth wave with interruptions (dead time) between each sweep, so it is not CW.

The one you are talking about has also used another very interesting waveform, it had an interrupted sweep, but unlike traditional interrupted sweeps it was not stopped at one end or the other, but in the middle. I only saw it used one time, for one stepping cycle. I am not 100% sure it is the same system, but there were some strong indicators it was. I have a video of it here:
https://www.youtube.com/watch?v=436kdnSgjjM

I will put up a vid of the more "normal" waveform for this system in the future, I have several I/Q recordings of it, just need to pick out the best to use. The "normal" waveform is interrupted LFMCW, but with the initial sweep starting mid freq, instead of at the high or low freq, again, unusual.

T!
 
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Token

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brandon,

I finally got around to posting a video of this system. I am almost certain it is an atmospheric radar / sounder of some kind, and not meant to track man made stuff. The revisit rate is just too slow and the frequency steps indicate a search for slowly changing conditions.

The most typical cycle seen is 1 min 45 secs on each freq, stepping up in frequency about 400 kHz per step. Revisit rate varies, but typically not faster than 3 times an hour.

In the video I show pictures of each detected sweep, it uses a very unusual 2 sweep burst sent 8 times a second. Even more unusual than the 2 sweep burst is the fact that the sweeps are half, full, half, instead of 2 full sweeps.

The combination of all of this gives it a pretty unique sound, you can hear the 40 Hz repetition rate (25 msec per full sweep) of the individual sweeps, combined with the on off nature of the 8 Hz burst rate. And the 800 kHz / sec chirp of each sweep is adding extra audio features also.

Video:
https://www.youtube.com/watch?v=jOn35JKU3CM

T!
 
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