[time-nuts] Testing frequency using NTP

[Steve Rooke]

I'm wondering about the possibility of checking the frequency of my
oscillator by using a NTP synced RT Linux system. What I'm thinking of
doing is building a long chain of dividers feeding a standard freq
counter in totallise mode such that I can count the number of cycled
over a long time period. What I would then do is to gate this with the
Linux system to measure the number of cycles over that period. I
figure that although the exact point of gate switching would not be
very accurate, due to clock jitter and uncertain delays in the OS,
this error could be made insignificant, in terms of the possible
stability of the oxco, when the sampling period is large. Even
watching the NTP stats on my workstation, OpenSUSE 11, it seems to
remain stable within a few ms, now that it has been stabilised for
months, and on a dedicated real time Linux system I should be able to
switch the gate within ms of the correct time so these errors should
only affect the least significant bits of the counting chain. If I
make the sampling period long, say hours, this should push those
errors well down the ppm.

Anyone have comments on this approach please? Feel free to blow holes in it.

Thanks,
Steve
-- 
Steve Rooke - ZL3TUV & G8KVD
Omnium finis imminet