[time-nuts] Brooks Shera's GPS standard or HP Z3801A??

Dr. David Kirkby drkirkby at medphys.ucl.ac.uk
Tue Apr 26 07:55:18 EDT 2005

Poul-Henning Kamp wrote:
> In message <000801c549ca$7c106d80$b20ff204 at computer>, "Tom Van Baak" writes:
>>>Don't forget that a PRS10 Rb from eBay and a Oncore M12+T from
>>>synergy-gps.com would be both cheaper and more stable.

Why would it be cheaper than building Brook Shera's unit? You still need 
all the same electronics, but a more expensive oscillator (I assume the 
PRS10 is going to cost more than an HP 18011A.)

I can understand that it is probably likely the peformance will be 
better than that of the HP Z3801A, as I guess you can use a long time 
constant to keep the Rubidium on frequency, which would not be possible 
if using a crystal.

>>Good point. Has someone posted a Z3801A vs.
>>PRS10/M12+ comparison? I have a lot of data
>>on the PRS10 but haven't put an M12+ to it yet.

How does the short term phase noise of the PRS10's compare with the HP 
10811A? I guess in the long term, they will both be the same if you link 
them to a GPS source, but short term you have said will be dominated by 
the crystal oscillator.

I guess a current unit is likely to be better than a 20-30 year old one.

> I should add that with an UT+ the sawtooth has a tendency to
> throw the PRS10s PLL off kilter, even with the 256 second
> averager (because the sawtooth does not necessairly average
> out to zero in that timeinterval).
> Even then, the PRS10+M12+T is by far the best bang for the
> buck I can think off.

I am confused how this can be cheaper although I accept its performance 
should be excellent.

Dr. David Kirkby PhD CEng MIEE,
Senior Research Fellow,
Department of Medical Physics,
Mallet Place Engineering Building,
Gower St,
University College London,
London WC1E 6BT.

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