Unid PSK8 2400Bd serial waveform heard on 6987.0 KHz/USB, data transfers appear to occur in ARQ mode (Figure 1).
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| Fig. 1 |
The larger signal' segments have strong 66.66ms ACF spikes that make a 160-symbol framing consisting of 32 known symbols (mini-probe?) followed by 128 symbols of data.
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| Fig. 2 - 66.66ms ACF and relative 160-symbol frame |
The analysis of the frame' symbols (Figure 3) reveals that the mini-probes consist of a 16-symbol sequence which is repeated two times.
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| Fig. 3 - analysis of the frame symbols |
Short segments too, maybe ACKs or some other negotiation messages, are PSK8 modulated and have a period of 768-bit/256-symbol length: at glance, it looks like a Walsh Orthogonal modulation mode (Figure 4).
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| Fig. 4 |
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