14 November 2015

Chinese 30-tone LSB/USB waveform

These signals has been heard on 13 November on 16497.0 KHz USB (16500.0 KHz LSB) at 1420z, transmission was noised and of poor quality but this does not prevent a good study.
The preamble is composed of four QPSK modulated tones, 600 Hz shifted, starting from 650 Hz (USB tuned, Pic. 1). The pilot (doppler) tone is located in the higher part of the spectrum at 2550 Hz. The waveform uses 30 orthogonal subcarrier tones, 75 Hz spaced, with BPSK modulation and symbol rate 60 symbols/sec (Pic. 2) and it is transmitted in burst mode. The recording has been resampled at 7200 Hz, getting a better value for the "magic k" factor (=1/4). The whole waveform, 30 carriers + pilot tone, spreads ~2450 Hz.
As shown in Pic. 3, the waveform has exactly the same characteristics and the same OFDM values of the Chinese 30-tone, except for:
- the preamble and the position of the pilot tone (due to LSB/USB switch);
- the lenght of the bursts.

More likely this is the Chinese OFDM 30-tone "burst" with an amended lenght of the bursts, as Alipio pointed in his comments. Just as a final note, looking at the table in http://www.radioscanner.ru/info/article538/, this waveform is very similar to the one called as "MARCONI" (Pic. 4). 
Recording is availabe by a simple request.

Pic. 1
Pic. 2
Pic. 3
Pic. 4

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