[time-nuts] GPSDO Question
Poul-Henning Kamp
phk at phk.freebsd.dk
Mon Sep 3 20:06:03 UTC 2007
In message <c03.175890b6.340db548 at aol.com>, SAIDJACK at aol.com writes:
>); SAEximRunCond expanded to false
>This brings up another question: how good are true PID loops that also make
>use of the differential term (e.g. correcting for rate of change of the
>phase)? The literature talks about the differential term being hardly used in the
>industry because it can add noise and instability to a system...
I tried it and found that you could indeed et faster convergence, but
I did it with a HP5370B as phase comparator to minimize the noise.
With more realistic phase comparators I don't think it is sensible.
I personally prefer to start with a very short tempered PLL and then
increase the timeconstant as things get better.
The hard part is knowing when to stop increasing the time constant,
and I have found that keeping track of phase error zero crossings
is the best indicator: If you don't see any (for too long time),
your PLL has too long timeconstant.
Poul-Henning
--
Poul-Henning Kamp | UNIX since Zilog Zeus 3.20
phk at FreeBSD.ORG | TCP/IP since RFC 956
FreeBSD committer | BSD since 4.3-tahoe
Never attribute to malice what can adequately be explained by incompetence.
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