I wrote:
> I can reproduce this using EbSynth and a weak near-field
> 9th harmonic signal. 2 to 3dB loss every time on a similar
> strength signal to last night's test.
> There is also an error floor showing up, about 6 to 8% BER
> with a very strong signal ...
I tracked this down to a problem in my receive timing system,
the one that mixes the signal and PPS into a BT878.
With that fixed, I can no longer reproduce the anomaly here.
EbSynth checks out ok - measuring the output phase against a
GPSDO reference shows a phase jitter around 0.14 degrees RMS
at 53077.222222 Hz and the peak phase deviation on a run of
a few hours was only 0.34 degrees. The phase plot of a BPSK
transmission looks real good.
So maybe there's a problem with the multiplier, which uses
junk box parts and an unregulated supply. It wouldn't be too
hard for the thing to introduce an intermittent phase error,
eg by a fluctuating threshold of a Schmitt trigger or an
unstable capacitor.
--
Paul Nicholson
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