12 July 2018

MFSK-32 & OFDM 60-tone, a new "Serdolik" waveform ?

Interesting transmissions centered on 7659.0 KHz (7657.0/usb as tuning frequency) and picked up with a  KiwiSDR located in Northen Norway (Kongsdr).
Transmissions consist of MFSK-32 87Bd/97Hz and OFDM 60-tone 40Bd BPSK bursts, start and initial bursts likely act as  SOM/EOM and use a QPSK/PSK-8 2400 Bd modulation with 20ms ACF (ie 48 symbols). Both MFSK and OFDM bursts  are separated by 1900 ms and last 6000ms; the occupied bandwidth is about 3200Hz.
The OFDM bursts use the same MFSK-32 waveform as preamble and exhibit a clear 100ms CCF. Note the lack  of the usual 3300 Hz pilot tone. 
Likely it's a new waveform belonging to "Serdolik" family.

Fig. 1- MFSK-32 burts
Fig. 2 - OFDM 60-tone bursts
Fig. 3 - initial/final burst (SOM/EOM?)

The OFDM segment was observed also using QPSK modulation with a 225ms ACF

Fig. 4

Run a TDoA multilateration which showed Moscow area as the origin.


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