[time-nuts] time-nuts Digest, Vol 102, Issue 90

[David J Taylor]

Yep, been there, done that. I'm a Ham and have several receivers. However,
that method falls a bit short for what I think I need and have decided to
look for something a bit better. What has been unknown to me is what result
I might get if I take a GPS solution such as this:
http://www.adafruit.com/products/746 and add the antenna and such, plus
design a circuit to discipline one of the OXCO's I have. This unit does
have a 1 pps output. I suspect more than resolution to X digits, there's
also the question of whether a (low end) unit such as this will reliably
stay locked. On the other hand, if I purchase something off-the-shelf that
is good to 10 digits, at least I know what I'm getting. Thanks for your
reply.

Russ
K0WFS
============================================

Russ,

I have one of those units syncing one of my Raspberry Pis:

  http://www.satsignal.eu/mrtg/raspi1_ntp.html

It seems to keep lock with its own built-in antenna (no external one) and 
it's located on the second floor of a two-storey building, very near the 
ceiling and outside wall of a walk-in cupboard.  That's a north-facing wall 
as well, so I'm slightly surprised it does as well as it seems.  The 
cupboard is unheated, which improves the thermal stability compared to other 
stratum-1 FreeBSD & Linux PCs:

  http://www.satsignal.eu/mrtg/performance_ntp.php?period=week

PCs Pixie and Raspberry Pi #2 show offsets at 05:30 when the heating 
switches on.  PC Pixie is nearest to the radiator, and it shows! <G>

BTW: I would change the title if you reply to the digest.  I would have done 
that for my reply except /someone/ will complain!

Comparing that unit to a "timing" GPS shows it to be within 50 ns, but a 
timing GPS such as the u-blox LEA-6T from Synergy does give the figures for 
the sawtooth error in the PPS signal, and so should be better if that offset 
is used.

73,
David GM8ARV
-- 
SatSignal Software - Quality software written to your requirements
Web: http://www.satsignal.eu
Email: david-taylor at blueyonder.co.uk