[time-nuts] New topics (was Re: He is a Time-Nut Troublemaker....)

[Lux, James P]

> -----Original Message-----
> From: time-nuts-bounces at febo.com
> [mailto:time-nuts-bounces at febo.com] On Behalf Of Magnus Danielson
> Sent: Tuesday, December 23, 2008 9:26 AM
> To: Discussion of precise time and frequency measurement
> Subject: Re: [time-nuts] New topics (was Re: He is a Time-Nut
> Troublemaker....)
>
> John Ackermann N8UR skrev:
> > Magnus Danielson wrote:
> >
> >> My intent is to get some stuff done in the lab during the vacation.
> >> (Desperatly trying to get some more on-topic discussions going).
> >
> > Here are two questions that have been running around my head:
> >
> > 1.  Following on from the discussion last week about trying to
> > synchronize multiple oscillators to improve phase noise,
> I've wondered
> > about a simpler tack:  take, for example, two 5 MHz atomic
> standards
> > and mix their outputs together, using the 10 MHz result to drive a
> > time scale.  Assuming the standards were of relatively
> equal quality,
> > would this provide a better time scale than using one of
> the standards alone?
>
> I have been looking at mutual lock systems for say two 10 MHz
> oscillators. This mutual lock system behaves much as a PLL
> circuit (as contrary to the other mutual lock methods
> described previous) such that a phase detector detects the
> phase-difference between the oscillators, a loop filter
> filters this difference and then it is feed back with
> opposite signs to the respective oscillator. I envision that
> a common EFC input exists to the system. Such a system is
> kind of interesting in that within the PLL bandwidth, the two
> oscillators are locked and you see the average of frequency
> errors etc. Well above the PLL bandwidth the two oscillators
> is independent of each other and just above the PLL bandwidth
> they are essentially independent. As the two oscillators is
> phase-locked in, their outputs can be combined and noise
> reduction can be achived, which is the significant effect
> above the PLL bandwidth.
>

This is similar to the problems of synchronizing multiple AC generators connected to a common bus. In that application, you typically adjust the throttle on the prime mover (or penstock gate for hydro) for each generator, while keeping a stable system frequency.  This is a very difficult problem because of the nonlinearity and time delays inherent in the system, not to mention the fact that there's transmission lines involved and a varying load.  The transients on long transmission paths (like from pacific northwest to southern California) can take many hours to die out.

There have been notorious oscillation issues in days of yore.. Modern GPS disciplined frequency references makes it easier.. (rather than sync to each other, you all sync to a common master) As do DC links with inverters.


In your case, you're trying to do the mutual synchronization scheme.

Jim