[time-nuts] KD2BD WWVB receiver/decoder in QEX
Charles Steinmetz
csteinmetz at yandex.com
Mon Nov 23 00:24:25 UTC 2015
Hal wrote:
>It would be interesting to measure the propagation delay over a day
>or week, and watch the PLL error voltage over a scale of seconds or minutes.
Somewhere I probably still have miles and miles of paper tape that
came out of a WWVB phase comparator for many years BGE (before the
GNSS era). In addition to the slow tracks, which were recorded 24/7,
there were also fast tracks taken periodically. At the time, it was
the only practical way to maintain NIST traceability of time and
frequency measurements.
The take-home points from this data (at least for those of us who are
a half-continent or more distant from Ft. Collins) are (i) that the
propagation delay varies quite a lot -- 10s of ppm normally, more
during periods of unsettled space weather; (ii) that phenomena too
numerous to count contribute to the variability, so the resultant
error is a complex epicyclic function of phenomena with periods from
hours to years overlaid with random noise that can be much greater
than the cyclic variations; and (iii) that the amplitudes of many of
the lesser cyclic errors do not fall off rapidly compared to the
amplitudes of the stronger ones, so simple approximations of the
epicyclic features do not allow predicting the propagation delay more
closely than about tenths of a ppm (parts in e-7).
Been there, done that -- for many years -- and I'm very glad we're
rid of the need for it. Sometimes, progress is ... well ... progress.
Best regards,
Charles
More information about the Time-nuts_lists.febo.com
mailing list