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Shortwave Data Decoding - Discussions regarding decoding digital signals on the HF bands, including HFDL, ALE, RTTY, CW, and others.

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Old 01-28-2017, 1:43 PM
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Default signal on SW ,HF band

I hear a signal that sounds like a buzz / large fan motor running , what is it ? I thought a jammer like the buzz over Radio Marti but I never hear a normal broadcast signal under it ,with Radio Marti jamming I can hear Radio Marti under the sound.
This sound shows up everywhere in the band from 2.0 - 30 Mhz.,day or night. Naturally following where the best propagation is. It fades up and down like any SW signal. I heard this same signal when I was a kid in the 1950's on SW.
One place it seems to be most nights is 6845 Mhz , it looks like it occupies 5khz.
What is it ?

Al
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Old 01-28-2017, 5:38 PM
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Interesting question, Al. I do not know the answer unfortunately but I am inquisitive as to the answer you find out.
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Old 01-28-2017, 5:42 PM
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Have a listen to all the sounds on here...

The Sounds of HF

...and see if you can find yours.

If it's in the broadcast bands it's likely to be a jammer, otherwise it may well be a STANAG military encoded signal, quiet on AM but a 'rotating' sound on SSB. If it has a "tick" every second it's a wefax broadacst. If it's a noisy burst about a second or so it's a atmospheric sounder, very common.
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Old 01-28-2017, 5:53 PM
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Al what radio are you using? If you are using a SDR a signal plot (sometimes called a sonogram or spectrum plot) would go a long way in identifying the signal.

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Old 01-29-2017, 10:27 PM
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Quote:
Originally Posted by alok View Post
One place it seems to be most nights is 6845 Mhz , it looks like it occupies 5khz.
What is it ?
What mode are you listening to it in? How are you determining it is 5 kHz wide?

6843 kHz, USB mode, on a nightly basis, is a STANAG 4285 signal. It can sound something like what you are describing (depending on what receive mode you are using), and there are many S4285 signals across the bands. S4285 is just a tad under 3 kHz wide though, not the 5 kHz you are describing, but depending on what receive mode you are using (assuming not a waterfall display) it is easy to call it about 5 kHz wide.

STANAG 4285 is a digital mode used by NATO forces, and almost always encrypted.

S4285 was not around in the 50's, or even 60's or 70's, but there were other signals that sounded something like it during those times.

T!

Last edited by Token; 01-29-2017 at 10:45 PM..
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Old 01-30-2017, 8:56 AM
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I might also add that the USCG is using 6850 kHz for DRM transmissions every couple of weeks for 2 or 3 days at a time. This would be 10 kHz wide covering the range 6845 to 6855 kHz and sounding a bit as you describe. They have been on that freq the last couple of days, and will be moving off of it in about 3 hours (at 1600z on 30 January 2017).

However, they are not on this freq all the time, and will return to it in a couple of weeks, so I doubt that is what you are hearing.

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Old 01-30-2017, 9:07 AM
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For those that are curious - here are waterfalls for both DRM and Stanag4285

STANAG 4285 Waterfall - The RadioReference Wiki

DRM Waterfall - The RadioReference Wiki

I think Mike was using the Hoka decoder to generate these.

Rarely you'll see a report that someone snagged a S4285 signal running a test tape in the clear, but these are very few and far between, as Token implies.

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Old 01-30-2017, 9:16 AM
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If you happen upon a S4285 signal, there are a few packages that can supposedly copy this, as long as it's not encrypted, of course...see this page for more

STANAG 4285 - Signal Identification Wiki

and this from the UDXF (PDF file)

Some Notes on STANAG4285 - via the UDXF

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Last edited by ka3jjz; 01-30-2017 at 9:22 AM..
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