[time-nuts] GPS noise reduction
bruce.griffiths at xtra.co.nz
Sun Apr 6 17:19:11 EDT 2008
Tom Van Baak wrote:
>> Actually, in this application will a bit of interlocking not
>> hurt, as the two oscillators should longterm have the same
>> frequency and interlocking will pull them together to their
>> average frequency. If you further aid this interlocking by
>> externally couple them together for higher frequencies (up to
>> say 10-100 Hz) then you can sum their outputs and get a
>> reduced noise response, a 3 dB improvement. The noise
>> processes internal to the oscillators will be uncorrelated
>> where as the locking causes the signals to be in phase.
> This is very true. I saw that HP did this in their cal lab with a
> half-dozen(?) hand-picked 10811 in order to get a combined
> virtual OCXO with better phase noise than any one physical
> OCXO. Rick, maybe you remember some details of this cool
> 10811 ensemble?
Phase noise is also reduced when an oscillator uses several crystals
(with the same resonant frequency) connected in series.
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