Am 29.12.2017 08:51, schrieb Paul Nicholson:
I've examined the software at Forest and all appears to be
working fine, at least as well as my own.
OK Paul, thanks for working that out.
A near field reference for testing the phase stability is certainly a
good idea. It should be there all the time ideally. Then one could even
correct the faulty segments. A safety redundance.
If we see distant
MSK phase changing (which we probably will), is it caused by
the rx or the propagation? Alpha signals are a bit tricky
to use when there are two transmitters interleaved in the
signal being averaged.
In my Alpha RDF spectrogram, the colours (indicating the phase) are
reproducing day by day quite nicely. There are 2 glitches. One is when
the TX switches the phase at 0 clock Moscow time. The other glitch is at
0 UTC. Then there is the slow change of the phase between day and night.
I am in another location and it is another path though.
Perhaps just the weakness of the signal at Forest?
Eb/N0 -0.1 = S/N 7.5 dB in the 30.6 uHz bandwidth in
which the phase is measured.
Could be the reason. But you are comparing just 2 or 3 days. On my 1
character message at 17470.1 Hz there were no unexpected phase changes
Another idea could be a damage in an electrical component in the high
impedance preamp. Maybe a water drop that changes the capacity
somewhere, leading to a phase shift. This would not affect the timing
but the phase Just a guess.
I find it most useful to get an overview of the system performance by
looking on a 'wideband' spectrogram, covering e.g. 0...24 kHz and half a
day or a day. You will immediately see if something changed, like the
signal levels, the phase and timing and sample rate correction (when
running an Alpha plot for example). Or you will see if a new QRM source
appeared or disappeared. All this without a particular search for
eventual errors, just the usual daily view on that spectrogram. I would
feel blind without that :-)
So in the end, is it propagation or not? For me it sound unlikely that
it is propagation. On 17.4701 kHz, over such a distance, maybe. But not
on 8270 Hz on the path between VO1NA and Mike.
Uuh, another strange idea: Maybe a faulty component in the preamp that
changes the phase frequency dependently, like a capacitor moving the
edge frequency of a LPF or HPF and changing the phase hereby?
73, Stefan
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