[time-nuts] GPS: ADEV or MDEV?
Dr Bruce Griffiths
bruce.griffiths at xtra.co.nz
Tue Apr 24 03:49:31 UTC 2007
SAIDJACK at aol.com wrote:
> Hi Bruce,
>
>
> in an 'uncontrolled' environment like that one would not get 2-20ppm retrace
> on the Zener (as speced in the table sent to this group earlier) I would
> think.
>
> bye,
> Said
>
Said
Yes it could be worse.
What I'm trying to show is that the thermal environment of the EFC
reference and DAC is important as is their noise.
Just low pass filtering a PWM waveform whose amplitude is determined by
a noisy supply regulator, as some do, is just too noisy to obtain
optimum performance from a 10811 or equivalent performance OCXO.
Of course one can always resort to annealing out the retrace by
controlled thermal cycling of the reference as Fluke (optionally) do in
their 7000 series references whenever continuous power is lost.
These 10V references use selected LTZ1000's to achieve a drift of around
1ppm/year.
Bruce
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