[time-nuts] 10 MHz over optical fiber?

[Didier]

> -----Original Message-----
> From: time-nuts-bounces at febo.com 
> [mailto:time-nuts-bounces at febo.com] On Behalf Of Bruce Griffiths
> Sent: Wednesday, November 26, 2008 6:56 PM
> To: Discussion of precise time and frequency measurement
> Subject: Re: [time-nuts] 10 MHz over optical fiber?
> 
> Didier wrote:
> > If your concern is simply a stable frequency reference, 
> that's true, 
> > even though I am not sure what kind of cleanup oscillator 
> would match 
> > the short term stability of a maser. But also if you want 
> to use it as 
> > a time standard, the phase shift in the fiber has to be 
> compensated, 
> > and it's variations over temperature/humidity/gravity and 
> whatnot must 
> > be accounted for.
> >
> > This is time-nuts, we don't simply want to make things 
> work, we want 
> > to make them work good :-)
> >
> > Didier
> >
> >   
> Didier
> 
> A linear temperature ramp will create a linear ramp 
> (equivalent to a frequency shift) in the fiber delay.
> Such temperature ramps may be expected at least twice a day. 
> In other words the the rate of change of temperature needs to 
> be low to preserve the frequency accuracy at the receive end 
> of the fiber.
> 
> Bruce
> 

Bruce,

Over a 34 km path, one should expect temperature variations not to be
uniform (unless the fiber is buried, but over 34 km, that would be
expensive), so simple open loop pre-programmed compensation would probably
not work well, some form of active, dynamic compensation should probably be
used.

Didier