[time-nuts] LTE-Lite module
SAIDJACK at aol.com
SAIDJACK at aol.com
Mon Oct 20 23:07:07 UTC 2014
Thanks much Charles,
just to remind everyone that the main idea of making the boards available
was to get folks a good disciplined TCXO, not to work as a development
platform to discipline external OCXOs.. Also as mentioned in the FAQ, the
typical performance plots I have been sending and are also in the user-manual
are gathered under optimal conditions of course: a roof-top antenna, units
shielded from airflow, and units running for a couple of days before testing.
Please also note that I tried an OCXO with only +/-2Hz EFC range and it
did not lock due to the ~10Ks resulting time-constant and the loop being way
to slow to capture the OCXO..
External oscillators should have between 9Hz per Volt to 100Hz+ per Volt
EFC sensitivity from what I can tell, otherwise an OPAMP circuit would be
needed to bring the EFC into that range. Sorry, I cannot propose such a
circuit, but such a circuit had been sent as a schematic to the time nuts some
years ago by someone if I remember correctly.
In a message dated 10/20/2014 15:55:45 Pacific Daylight Time,
csteinmetz at yandex.com writes:
>here is the ADEV plot from my overnight test with the DOCXO. * * *
>This was done without any loop adjustment whatsoever, same board and
>software that drives the on-board TCXO. I will let the result speak
>save to say the loop, the DAC, the DAC reference, and the GPS with a
>OCXO can achieve performance at a level approaching two orders of
>magnitude better than our spec which is 1ppb for this particular product.
Thanks for the ADEV plot, Said -- more pertinent for most time nuts
purposes than PN. Of course, the typical performance of the LTE-Lite
with the TCXO is significantly better than the spec (according to the
user manual, about 5e-11 at 1 second and 1e-10 at 10 seconds, already
1 to 1.5 OOM better than spec), so the typical improvement with the
OCXO wouldn't be a full two orders of magnitude. Still, very
noteworthy performance that *surely* justifies time nuts in buying
one of the good, cheap OCXOs flooding the surplus market to go along
with their LTE-Lite. Good show.
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