[time-nuts] The best GPSDO ?

[Bruce Griffiths]

Ulrich Bangert wrote:
> Gentlemen,
>
> I know that lots of you own a GPSDO, some of you two or even more. For that
> reason I conclude that there must be a lot of knowledge available on how
> different GPSDOs perform against each other. This is why I want to put
> forward the question for the BEST GPSDO in terms of
>
> a) phase noise up to 100 kHz from the carrier
>
> b) AD for tau>  0.1 s and<  say 7200 s (where the AD is controlled by LO AND
> GPS and not by GPS alone)
>
> The basic question is: If we want a reference that can be used for phase
> noise measurements as well as for AD measurements, what shall we buy? If you
> come to the opinion that a) and b) cannot be satisfied by the same device,
> then suggest different devices that you would use for a) and b).
>
> My personal guess is (without owning one) that a Z3815 may be a candidate
> due to its E1938 oscillator.
The phase noise floor of the E1938 isnt all that low and there is an 
"interesting bump" in the region above a few kHz offset.
If you want I can send you the data obtained using a Timepod with dual 
reference sources.
The Z3815 PN floor should be somewhat higher due to its relatively low 
output signal level.
The spurs due to the internal switching regulators may also be interesting.
> But as to be seen on Tom's pages there are
> better and worse specimen of this OCXO too. My own measurements with the new
> Timepod indicate that my Z3805 with the MTI260 OCXO can't be that bad. You
> may even have luck with a double oven HP10811 in a Z3801 although the 6
> channel gps receiver is surely not state of the art. Perhaps the Thunderbolt
> is the solution?
>    
The thunderbolt phase noise floor isn't stellar due principally to the 
noisy output buffer amp.
However the PN floor of the OCXO used in some Thunderbolts can be quite low.
> I will be glad to read what you judge!
>
> Ulrich Bangert
> www.ulrich-bangert.de
> Ortholzer Weg 1
> 27243 Gross Ippener
>
>
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>    
Bruce