[time-nuts] Designing and building an OCXO and GPSDO
bruce.griffiths at xtra.co.nz
Wed Aug 13 00:01:42 EDT 2008
SAIDJACK at aol.com wrote:
> Hi Bruce,
> do you have any phase noise/stability measurements for these circuits?
No, I have no way of measuring phase noise at present.
Nor can I yet measure ADEV with adequate sensitivity and stability.
However the phase noise floor can be estimated to within a few dB.
Its even possible with some effort to estimate the phase noise of the
buffer amplifiers in the flicker region.
If low phase noise buffer designs are used the phase noise floor depends
(for a CB input stage) on the buffer equivalent input current noise and
the crystal current.
With sufficient crystal current the phase noise floor can be very low
A phase noise measurement system would be useful for optimising the
close in phase noise.
The circuits are intended to be somewhat better than a gate oscillator
but without the complexity involved when AGC is used.
The original request design was intended for a fundamental mode oven
crystal the drift of which is unlikely to be very low.
Nor will the Q of such a crystal be particularly high.
With an overtone crystal a means of suppressing oscillation at unwanted
overtones is required.
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