[time-nuts] 5370B on eBay, carrier phase tracking GPS receiver

Magnus Danielson cfmd at bredband.net
Mon Feb 19 05:12:20 EST 2007


From: Dr Bruce Griffiths <bruce.griffiths at xtra.co.nz>
Subject: Re: [time-nuts] 5370B on eBay, carrier phase tracking GPS receiver
Date: Mon, 19 Feb 2007 17:41:52 +1300
Message-ID: <45D92A90.307 at xtra.co.nz>

> Magnus Danielson wrote:
> >> http://tycho.usno.navy.mil/ptti/ptti99/PTTI_1999_405.PDF
> >>     
> >
> > There is another paper just before it. There is also a patent for a 
> > specific
> > form of implementation.
> >
> >  
> >> Note they used an Oncore VP, the Superstar has a better carrier phase 
> >> tracking.performance.
> >>     
> >
> > What they did was that they hooked their Oncore VPs up to cesium beams 
> > for
> > test purposes. Locking that clock with a not-so-perfect but sufficient 
> > for
> > the task ratio.
> >
> > You can do about the same without too much difficulty, but the Allstar,
> > Superstar and Superstar II receivers belong to those that is built out 
> > of the
> > Zarlink chipsets 
> An interesting product originating from Mitel (Mike and Terry's 
> lawnmowers later became MITEL - according to their local rep about 20 
> odd years ago)

Hehe... yeah, I know it was in the Mitel days they started this. I even beleive
that the GPS stuff came in with another buy, but I don't recall the details.
The Zarlink reference is more relevant for initial attempts to dig up
datasheets, where as Mitel is usefull for some of the older material.

> > which all feature an interesting issue, the use of a 10 MHz
> > TCXO. Now, this frequency should be fairly know to us time-nuts, no? ;)
> >
> > Wiring in an externally supplied 10 MHz should not be all that difficult.
> > The receiver is now effectively a high resolution phase comparator 
> > between the
> > selected sats and the timing source used for reference. The PPS output 
> > of the
> > receiver is not used for reference, but rather the carrier phase 
> > pseudo-ranges.
> > Either you tap the pseudo-range data out and do the dirty stuff 
> > outside, or
> > you have the receiver do all the calculations. Having a reciever do some
> > interesting corrections on pseudoranges may be a bit harder thought.
> >
> > Anyway, if you do things properly, it will be a much better solution than
> > looking at that PPS.
> >
> >   
> However if all you have is a 10811 it will limit the short term 
> satbility of such a GPSDO.
> The phase carrier measurements will have a lower noise floor than the 
> 10811 for tau > 10s or so.
> A better oscillator (FTS1200, FTS100 Oscilloquartz OSA8607 etc.) will 
> have a significantly lower noise floor.

Indeed. Carrier phase will cut in early as the quieter source than the PPS
method.

> However since the latter generally have 5MHz outputs a low phase noise 
> frequency doubler is required.

Indeed. Some are however available in 10 MHz.

Also, the carrier phase method is usefull for rubidium and cesium comparisions
not to speak about hydrogen maser (not a relevant problem just yeat).

Cheers,
Magnus



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