Hi Tom:
That makes sense because the GPS was just coming on line and not anywhere near a full compliment of satellites and SA
was on.
HP had some way around SA that improved the timekeeping.
Has that ever been disclosed?
Have Fun,
Brooke Clarke
http://www.PRC68.com
http://www.end2partygovernment.com/2012Issues.html
Tom Van Baak wrote:
Hi Brooke,
True, except that in most cases the long-term frequency drift rate is so tiny compared to
all the short- and mid-term instability that it is not worth worrying about. In other
words, I agree it is modeled as a "linear ramp", but the ramp, even at huge
timescales, is so close to flat, what's the point?
Look at the output of a typical OCXO. Short-term the frequency varies by tens
or hundreds of ps/s; that's parts in 10^11 or 10^10. By contrast, you have wait
an entire day or week before you get that level of frequency error due to drift.
When you're in a rowboat outside SF bay, it's the 3 m waves every 5 to 10
seconds that you need to steer against, not the 3 m tides that occur gradually
over 12 hours.
Can someone show me a counter-example? Why is it better to include aging rate
into the PID. What quantitative improvement in performance does this actually
represent? I don't disbelieve it, I just have never seen the numbers.
One case where knowing the aging rate is important is during multi-hour or
multi-day holdover. Perhaps that's why HP included the 128-hour circular record
of frequency/aging into their firmware.
/tvb
Hi:
AFAICR the HP GPSDOs included the idea of measuring the aging rate of the
crystal and applying that correction during
holdover.
This was also mentioned by Brooks Shera in relation to his GSPDO (there was a
plot), but I don't think it was part of
the firmware?
So rather than just locking the control voltage to the last used value it would
be much better to add a linear ramp.
<http://www.rt66.com/%7Eshera/>
_______________________________________________
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.
_______________________________________________
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.
