Wednesday, September 18, 2019

>3 kHz wide bursts around 6300 kHz

This morning, a number of >3kHz wide bursts were noticed around 6300 kHz on a KiwiSDR in Europe. 

Below, one such burst is shown in terms of 576 symbol frames (5 samples/symbol sampled at 24 kHz -> 4800 symb/sec). The color indicates abs(z): (1) there are 6 individual bursts grouped together, and (2) a repeating sequences of symbols is present in each burst.

one 4800 symb/sec burst consisting of 6 individual bursts

The repeating sequence of symbols, extracted from multiple bursts, is shown below. This sequence consists of 64 BPSK symbols

It can be verified that the first 63 of these bits are generated by an LFSR and that the last bit balances the number of 0s and 1s, i.e., including the last bit there are 32 0s and 32 1s.

Top: the color indicates arg(z); bottom arg(symb) for a few of the frames shown on top.
Each burst starts with the same, 64 symbol long preamble that is immediately followed by the known sequence of symbols described above.

Unfortunately, the signal suffered from selective fading, so the modulation of the other parts of the bursts could not be determined.

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