[time-nuts] GPS noise reduction

Tom Van Baak tvb at LeapSecond.com
Sun Apr 6 12:04:28 EDT 2008

> 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?


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