[time-nuts] GPS noise reduction

Magnus Danielson magnus at rubidium.dyndns.org
Sun Apr 6 17:28:42 EDT 2008


From: Bruce Griffiths <bruce.griffiths at xtra.co.nz>
Subject: Re: [time-nuts] GPS noise reduction
Date: Mon, 07 Apr 2008 09:19:11 +1200
Message-ID: <47F93E4F.2040502 at xtra.co.nz>

> 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?
> >
> > /tvb
> >
> >   
> Tom
> 
> Phase noise is also reduced when an oscillator uses several crystals 
> (with the same resonant frequency) connected in series.

Yes, but it only reduces crystal related noise... where as amplifier noise is
not reduced.

Cheers,
Magnus



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