18 March 2014

Decoding pocorgtfo03.pdf with multimon-ng

Having had a read of pocorgtfo03.pdf (you can get it from here) and learning of its chameleon-like properties, I resolved to investigate the claim that "Treated as single-channel raw audio, 16-bit signed little-endian integer, at a sample rate of 22,050 Hz, it contains a 2400 baud AFSK transmission".

I'd already confirmed that the pdf looked like a JPG using the file command:

$ file  Downloads/pocorgtfo03.pdf
Downloads/pocorgtfo03.pdf: JPEG image data, JFIF standard 1.01, comment: ""
 I had a look at the file with baudline:


Sure enough the file seemed to show a modem signal at around 6 seconds in.  I remembered that multimon-hg could decode AFSK2400 and had a stab at decoding the tones with that:


$ multimon-ng -t raw -a AFSK2400  Downloads/pocorgtfo03.pdf -q
 POCSAG512 POCSAG1200 POCSAG2400 EAS UFSK1200 CLIPFSK AFSK1200 AFSK2400 AFSK2400_2 AFSK2400_3 HAPN4800 FSK9600 DTMF ZVEI1 ZVEI2 ZVEI3 DZVEI PZVEI EEA EIA CCIR MORSE_CW DUMPCSV SCOPE
AFSK2400: fm PASTOR-0 to APRS-0 via WIDE1-1,WIDE2-1 UI  pid=F0
:EMAIL    :pastor@phrack.org I have POC to share.

Nice!

12 March 2014

Psychedelic SSTV on 255.560MHz

I was having a rummage around in the UHF Satcom band when I noticed an unusual signal on the 255.550MHz transponder downlink.


It turned out to be analogue SSTV, Robot 36 mode, over FM centred on 255.560MHz.


It seems to repeat the same image for quite a while.  So far it has sent these pictures, received with QSSTV:
 




The colour looks worse than NTSC :P  I'm not sure why it is so bad.  Similar reports have been noted here and here (forums.radioreference.com) and on youtube here.

2 March 2014

QSSTV with hampal digital SSTV

I've been trying out the new version of QSSTV, 8.2.4, listening on on 40m.  It has support for the DRM-based digital modes now.

You can get the new version here.  Here are some screenshots: