Probably a simplex transmission heard on 6246.5 KHz/USB. Although the SNR is poor, it's possible to see a central un-modulated tone a + 1500Hz that splits the signal in two identical parts which I analyzed separately. The results show an OFDM modulation of 12 + 12 tones at a rate of 48 symbols/sec; the on-air constellation seems to be QPSK on each channel.
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| Fig. 1 |
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| Fig. 2 |
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| Fig. 3 |
The initial part exhibits an upper un-modulated tone and a short FSK
Modem name and users are unknown to me.
Update:
thanks to hf_linkz who pointed me to the correct identification of this modem: it's the "Marconi 25-tones" as depicted here:
http://signals.radioscanner.ru/base/signal125/
https://www.sigidwiki.com/wiki/Marconi_Selenia_25-Tone_Modem
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| Fig. 4 |
Modem name and users are unknown to me.
Update:
thanks to hf_linkz who pointed me to the correct identification of this modem: it's the "Marconi 25-tones" as depicted here:
http://signals.radioscanner.ru/base/signal125/
https://www.sigidwiki.com/wiki/Marconi_Selenia_25-Tone_Modem
