[time-nuts] TIC resolution impact on GPSDO's performance
phk at phk.freebsd.dk
Mon Dec 25 04:32:11 EST 2006
In message <458F1D50.3000707 at xtra.co.nz>, Dr Bruce Griffiths writes:
>> We know that the hardware PPS signal from gps is phasemodulated
>> with a +/- N ns signal which has a box distribution and upper
>> frequency limit of 2 Hz and which, subject to temperature stability
>> and hanging bridges, has no significant frequency components below
>> < 1/500s.
>Has this been established by actual measurement?
With the caveat that I wrote 2Hz instead of 0.5Hz (Nyquist thing)
this follows directly from signals theory.
Running a FFT over the negative sawtooth values is an interesting
exercise, in particlar of you collect a weeks worth of data or more.
>Ignoring the combined effects of quantisation and coherence would not
>seem to be very sensible.
A quantum of 1ns is not a concern if the attack point for the PLL
is on the order of hours.
I'm not sure what coherence you are talking about here, the
negative sawtooth signal is not coherent with anything as far
as we know.
>> A less significant difference from PID regulations is higher order
>> integrals: They are not useful for temperature regulation,
>This is not true, using a second integrator in a crystal oscillator
>temperature regulation loop can be very effective, as indicated in the
That does make sense, I was only talking about more normal
temperature regulations (water tanks, process chemicals etc).
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