[time-nuts] GPS noise reduction
didier at cox.net
Sun Apr 6 10:13:02 EDT 2008
> -----Original Message-----
> From: time-nuts-bounces at febo.com
> [mailto:time-nuts-bounces at febo.com] On Behalf Of Magnus Danielson
> Sent: Sunday, April 06, 2008 6:18 AM
> To: time-nuts at febo.com; bruce.griffiths at xtra.co.nz
> Subject: Re: [time-nuts] GPS noise reduction
> 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.
That's an interesting concept. One could couple a number of oscillators that
way (provided it is practically feasible) and improve phase noise, like you
can make a better LNA by paralleling several amplifiers.
For that to actually be beneficial however, the locking effect should be
mutual, i.e. each oscillator has the same effect on the other so that
"averaging" (probably not the right term, but you get the idea) takes place.
If coupling is assymetrical, then the dominant oscillator (the one that is
less affected by the others but affects the others) will drive the result
and you won't have any improvement over that oscillator alone. Since it is
very hard in practice to control coupling between two devices unless you do
it intentionaly (that means the devices are designed to be coupled in a
controlled fashion), it may be best (easier in practice) to do everything
you can to reduce coupling.
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