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21 MHZ DX pile up - screen shot and WAV file

Posted: Tue Feb 03, 2015 3:10 pm
by DaveB
They are going absolutely nutty on 21 Hz! and I have no idea who they are working - I suspect the DX station is working split frequency - but it makes a good screen shot!

Also an 11 second long .wav file of the pile up. It is rather large as it is a full 5 MHz bandwidth. You'll have to zoom in to see it. It was recorded from HDSDR

If you look at the full bandwidth you'll see a very strong signal spanning 21.58 to 21.71 MHz. It looks like a sub-harmonic of a DAB signal - which I'm trying to track down - but the shape of the signal doesn't match any of the DAB Muxes. I have a DAB pre-amp (12dB gain) and I when unplug all the aerial leads from the output it is still 25dB above the noise floor - but disappears as soon as the power is switched off. So I suspect it is the pre-amp - and has nothing to do directly with breakthrough. Although some of the signals are peaking over 60dB above the noise level no sign of them appearing on the other side of the centre frequency and no signs of this on SDR Sharp or SDR Console.



Re: 21 MHZ DX pile up - screen shot and WAV file

Posted: Tue Feb 03, 2015 6:52 pm
by Quimquim
Hi DaveB,
looking at your picture and the frequency it look as a HAM CW band.

In CW mode you can a bunch of transmitter close together who may look as a digital transmission.

I don't know in what region you are but in america, the frequency of your picture, fall exactly in the 15 meters CW HAM band.

PS: I have tried to play your audio file but I have no sound.

See the extract below from the American Radio ARRL site ( )

15 Meters
Novice and Technician classes:

21.025-21.200 MHz: CW Only

General class:

21.025-21.200 MHz: CW, RTTY/Data
21.275-21.450 MHz: CW, Phone, Image

Advanced class:

21.025-21.200 MHz: CW, RTTY/Data
21.225-21.450 MHz: CW, Phone, Image

Amateur Extra class:

21.000-21.200 MHz: CW, RTTY/Data
:idea: ======= 21.200-21.450 MHz: CW, Phone, Image ====== :idea:

Stay tuned !!!!! :lol:


Re: 21 MHZ DX pile up - screen shot and WAV file

Posted: Wed Feb 04, 2015 9:51 am
by DaveB
Hi Quimquim,

Thanks for suggestion - but the big rectangular block I'm talking about is to the HF side of the 15m amateur band. At 21.58-21.71 and I've also found the same block at double the frequency around 43 MHz and twice as wide. Zoom in a lot and you can see it is one transmission.

BTW did you play the wav file back through SDR software as it actually a recording of raw RF



Re: 21 MHZ DX pile up - screen shot and WAV file

Posted: Wed Feb 04, 2015 2:42 pm
by CaptainNemo
Hi there DaveB, for your next post about "listening shortwaves" (let say 3-30MHz)
it would be a nice thing if you join us on this thread:

I'm a simple end-user but I think keeping some order is useful for us all.
Not mandatory, of course... :lol:

Re: 21 MHZ DX pile up - screen shot and WAV file

Posted: Wed Feb 04, 2015 11:57 pm
by Quimquim
Hi DaveB,
I took a look at the wav file on HDSDR. This modulation look to be some kind of FSK.

I've tried to pass it through Fldigi with many protocol but didn't find what it is. It's not simple to tell if it's a single transmission or many, close together.

By the way what kind of antenna are you using? What is your setup?

It look to perform quite well with a very good s/n ratio.

Actually I have a poor man antenna ( a short length of wire hooked to the metal bar of a horizontal store ). :cry:

It's winter here in Quebec so not practical to experiment outdoor antenna with so much snow.

I'm actually looking for a not too much expensive one and easy to use in urban area. Don't have the space to extend many meters wire.

I have a look on the popular PA0RDT who have good critics.