Dear LF group,
A number of people expressed an interest in my reception of G4JNT's PSK
beacon, so here is 1/2 hour from the spectrogram from Monday night,
hopefully edited down to a reasonable size for the reflector.
As you can see, the phase transitions show up as "beads" on the carrier (
with Spectrum Lab I used 11025 sample rate, divided by 4, and 65k FFT
length to get 0.042Hz resolution - what I would usually use for 30sec
dots). Note there is a time lag between the 30s markers and the phase
transitions, presumably due to the time taken for the FFT to acquire
samples. To find the data sequence, we know that the first logic level at
the end of the period 21:00:00 to 21:00:30 is a 0; we can see a phase
transition occurs at the beginning of the 21:00:30 to 21:01:00 period, so
that the second data bit must be 1 - and so on for all 30 bit periods. If
there is a phase transition at the beginning of a bit period, the data in
that bit period is inverted from the previous data bit; if no transition,
the data is the same as the previous period.
Cheers, Jim Moritz
73 de M0BMU
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