This signal was recorded tuning 5308 Khz and using some KiwiSDRs from the northeast of the US, mainly the one owened by K3FEF in Milford (PA). Since its various operating modes and its uncommon parameters, we decided to study it a little more thoroughly, leaving out the transmission purposes and the hypothetical users. The duty cycle of the signal is quite low so it took several hours of recording to collect signals suitable to be analyzed.
In the spectrogram of a recording we can see the bandwidth of the modes (Fig. 1). When several consecutive segments are transmitted, the separation between them is about 3m30s and the duration of the segments ranges between 94 and 106 seconds.
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| Fig. 1 |
mode 1
This mode has a spectral occupation of one 1000 Hz. The modulation is QPSK although with a notable majority of the symbols 0 and 2 and a speed of 600 Baud (Fig. 2). The ACF can be 840ms or 800ms and does not seem to transmit information, but seems to be idling. After demodulation, bits aligned in frames of 1008 bits for ACF of 840 ms and 960 bits for ACF of 800 ms (Fig. 3).
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| Fig. 2 |
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| Fig. 3 |
mode 2
Its spectral occupation is about 1600 Hz. The modulation is QPSK with the same structure of mode 1, with a speed of 1200 Baud and an ACF of 420ms or 400ms. Also this mode exhbits a 1008 bits (960) frame with a very similar structure (Fig. 4).
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| Fig.4 |
mode 3
The modulation speed is 1200 Baud with a spectral occupancy of about 1400Hz. It is a GFSK with a shift of about 800 Hz andACF of 840ms or 800ms. The binary frame has a 1008 or 960 bits length (Fig. 5).
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| Fig.5 |
mode 4
The modulation speed is 300 Baud with a spectral occupancy of about 600 Hz. The modulation is an FSK with a shift of 400 Hz and an ACF of 3.35 or 3.2 seconds. Once demodulated, the frame is still 1008 bits or 960 bits just like the previous ones (Fig. 6).
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| Fig. 6 |
