Hi, from 11-10-2022 19:39 Dutch local time , so 17:39 UTC till about 14 hours later I recorded the 436 MHz satellite band from Airspy 5 MHz wide with 6 el yagi pointing north and Upu 435 filtered preamp. This morning I did run the data file analyser from SDR Console with it and played back a lot of signals from the waterfall which was created. A screenshot from the signals is attached
Around 21:46 I notice some data type signals which I could easily play back from the recording and noticed the transmissions sound like pager type (pocsag ?) modulation. However my pocsag decoder shows no interest in this audio.
I randomly played some of the transmissions while recording audio in WFM, audio file attached.
I had my first view in the Satnogs DB for transmitters today but I don’t see a matching modulation type for the signals I do hear.
the dropbox link contains the MP3 audio recording.
We can try mulimon-ng -a POCSAG512 -a POCSAG1200 -a POCSAG2400 to try and decode this signal.
(C) 1996/1997 by Tom Sailer HB9JNX/AE4WA
(C) 2012-2022 by Elias Oenal
Available demodulators: POCSAG512 POCSAG1200 POCSAG2400 FLEX FLEX_NEXT EAS UFSK1200 CLIPFSK FMSFSK AFSK1200 AFSK2400 AFSK2400_2 AFSK2400_3 HAPN4800 FSK9600 DTMF ZVEI1 ZVEI2 ZVEI3 DZVEI PZVEI EEA EIA CCIR MORSE_CW DUMPCSV X10 SCOPE
Usage: multimon-ng [file] [file] [file] ...
If no [file] is given, input will be read from your default sound
hardware. A filename of "-" denotes standard input.
-t <type> : Input file type (any other type than raw requires sox)
-a <demod> : Add demodulator
-s <demod> : Subtract demodulator
-c : Remove all demodulators (must be added with -a <demod>)
-q : Quiet
-v <level> : Level of verbosity (e.g. '-v 3')
For POCSAG and MORSE_CW '-v1' prints decoding statistics.
-h : This help
-A : APRS mode (TNC2 text output)
-m : Mute SoX warnings
-r : Call SoX in repeatable mode (e.g. fixed random seed for dithering)
-n : Don't flush stdout, increases performance.
-j : FMS: Just output hex data and CRC, no parsing.
-e : POCSAG: Hide empty messages.
-u : POCSAG: Heuristically prune unlikely decodes.
-i : POCSAG: Inverts the input samples. Try this if decoding fails.
-p : POCSAG: Show partially received messages.
-f <mode> : POCSAG: Overrides standards and forces decoding of data as <mode>
(<mode> can be 'numeric', 'alpha', 'skyper' or 'auto')
-b <level> : POCSAG: BCH bit error correction level. Set 0 to disable, default is 2.
Lower levels increase performance and lower false positives.
-C <cs> : POCSAG: Set Charset.
-o : CW: Set threshold for dit detection (default: 500)
-d : CW: Dit length in ms (default: 50)
-g : CW: Gap length in ms (default: 50)
-x : CW: Disable auto threshold detection
-y : CW: Disable auto timing detection
--timestamp: Add a time stamp in front of every printed line
--label : Add a label to the front of every printed line
Raw input requires one channel, 16 bit, signed integer (platform-native)
samples at the demodulator's input sampling rate, which is
usually 22050 Hz. Raw input is assumed and required if piped input is used.
Here an example I use to decode POCSAG in combination with GQRX udp out.
nc -l -u 7355 | \
sox -t raw \
-b16 -r 48000 - \
-b16 -r 22050 -t raw - | \
multimon-ng -t raw \
-a AFSK1200 -a FLEX -a POCSAG1200 -f alpha -
Hi Jan, I made a fresh recording of the same spectrum last night, I will have a look if the same signal appears again and make a small bandwidth IQ file of the pass. If it’s not there I will do the same from the recording from 4 days ago. Going to try if multimonng runs in WSL too
So the good news is the signal appeared again in the recording from 13-10 to 14-10, 20:18 utc time and a bit weaker. About 20 minutes earlier as the 2 days before, the 21:48 utc pass was almost unreadable in the waterfall.
So far no decodes with Multimon-ng, now recording the same frequency with only 625 kHz bandwidth.
Allright, played around with a short recording, to get the feeling. First I adjusted the gain for the rtl_sdr with rtl_tcp, settled for 22.9 dB. After running rfplot I notice I have to adjust Zmax to about 18 - 20, which I can use as fixed setting in the rfplot, but appears way off compared to the 0.01 or 0.05 values from the web instructions ?
Note that this rtl has no tcxo and is not compensated for ppm so the actual image has no value for any conclusions, just to show what I get.
So, indeed after some crash course and some “fun playing with strf” topic reading I managed to get both ISS on 437.800 and VZLUSAT-2 identified
So I did run the same on the recording for the 18th of October. used the -s to get the starting bin about 5 minutes before the transmissions where in my reach.
Tried with s to set, tried with D to set, but trace not identified so far.