Hi Tom,
On 04/16/2013 09:42 AM, Tom Van Baak wrote:
I wonder if one should only measure the PPS thought. Looking directly at
the clock could help to separate the clock drift and the time, even if
you get sufficient clues from the PPS and sawtooth correction.
Cheers,
Magnus
I've never tried that.
Tom, you scare me some times, this is one of them... or the time actually.
Start with checking the ADEV of the LO. I always assumed the 1PPS was
pre-compensated for instantaneous LO offset and rate, as calculated
during the previous second(s).
Well, it is... but it also solves the position-time each second and that
takes over. If you loose signal, that's when the predicted PPSes will
shine through.
If so and ADEV(1 s) is less than 1e-9 then the 1PPS + sawtooth will
have sufficient accuracy for your needs. Message @@Ha contains the
oscillator and clock parameters.
True. That get's you far. Just looking at that and bring it into your
model is also something you can do. It's interesting to notice that the
@@Ha message has a time (to nanosecond), and then clock bias and
oscillator offset and on top of that a delta correction in the @@Hn
message. Would be nice to know exactly how them all fitted together.
BTW. I hooked up my M12M-T to a Novatel 700 pinwheel just to check it
out again.
As you know professional receivers bypass this issue because they take an
external LO (e.g., Rb, Cs, HM).
Oh yes.
The TCXO sitting there looks like a RAKON thing, I haven't looked at the
details, but maybe it can be steered? It's interesting that the TCXO
temperature can be read out.
When you look at the actual clock solutions (which are in the @@Hn
message) you will be surprised at the variance. At the per-SV
per-second level it is not uncommon to see errors of many ns, even
tens of ns. But when you average up to 12 SV together every second
for 600 seconds then you start to see something trustable. You can
see first hand why GPSDO need long time-constants.
Here's a one second sample of a single Hn message:
@@Hn: sigma 36 sawtooth 10 0 0 00000000 mean frac 861564.000 (0.000)
ch 0 sv 6 frac 0.000861576 s = mean + 12 ns
ch 1 sv 5 frac 0.000861586 s = mean + 22 ns
ch 2 sv 10 frac 0.000861581 s = mean + 17 ns
ch 3 sv 19 frac 0.000861573 s = mean + 9 ns
ch 5 sv 13 frac 0.000861571 s = mean + 7 ns
ch 6 sv 26 frac 0.000019831
ch 7 sv 28 frac 0.000861555 s = mean + -8 ns
ch 8 sv 7 frac 0.000861548 s = mean + -15 ns
ch 9 sv 3 frac 0.000861571 s = mean + 7 ns
ch 10 sv 8 frac 0.000861546 s = mean + -17 ns
The urge to get into the dirty details got higher by that. Curious at
seeing a log of data.
Let's see if my M12M-T locks up in the current quick-hack setup.
Cheers,
Magnus
_______________________________________________
time-nuts mailing list -- time-nuts@febo.com
To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts
and follow the instructions there.
