[ntp:hackers] A stop-gap authenticated time service

Poul-Henning Kamp phk at phk.freebsd.dk
Sun Nov 15 11:12:42 UTC 2015


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In message <5648650F.1060502 at rubidium.dyndns.org>, Magnus Danielson writes:

>If I get the time, I might derive the various ADEVs for noise through 
>PLL. Might be a useful article.

You're provably better at math than me, so I'd probably not be a very
useful reviewer, but to the extent I can assist in any way, just yell
my way.

My personal "hands-on" experience is that the P term is invaluable
for initial capture, but once you're captured, it usually just adds
high frequency noise and for tracking you are better off with a
pure I regulator.

I'm not sure if this is why, but I do note that all of the HP506x
atomic frequency standards only use an I term.

When I realized that the NTP kernel-pll's P-term noise profile was
a source of instability, I started experimenting with different
"decay" strategies for the P-term.  I need to finish that and
publish the results and code.

Time, never enough of it...

-- 
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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