[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,
University College London,
London WC1E 6BT.
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