[time-nuts] LTE-Lite module
csteinmetz at yandex.com
Mon Oct 20 09:51:32 UTC 2014
>PLLs are really not that hard [context: we have been discussing
>all-digital PLLs ("ADPLLs")]
Yes, I know -- I have designed more than a few. I have also reviewed
more than a dozen hobbyist designs and modeled some of them, and
found that few hobbyists seem to have mastered the art. Judging also
by on-list responses over the years, it does not appear that many
time nuts are interested in designing and building their own
ADPLLs. So, I conclude that disciplining a good OCXO with GPS and
getting the best stability the OCXO can deliver is not practicable
for most hobbyists.
The OP in this sub-thread indicated that he was considering using an
LTE-Lite to discipline a "really good" 10811, and it appeared that
his expectation was to end up with a GPSDO more or less as good as
his 10811. My point was simply to put realistic bounds on the expectation.
Said posted that a quick lash-up with an OCXO produced stability
about 10x better than with the on-board TCXO. That is a useful
improvement, but a good OCXO (certainly, a "really good" 10811) will
have stability about 3 orders of magnitude better than a TCXO
(1000x), so two decades of possible improvement were not realized.
Said's experiment was a proof-of-concept exercise and not a careful
optimization, so it is almost certain one could do better than 10x
with some further work. But I very much doubt that optimization can
gain the entire two decades of potential improvement (short of
designing a full ADPLL, in which case you don't need the LTE-Lite at
all -- all you need is a source of PPS), and I doubt it is possible
to gain even one whole decade.
So, I am inclined to think that there are better (and easier) ways to
discipline a 10811 to reach its ful potential, that's all.
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