[time-nuts] Brooks Shera's GPS standard or HP Z3801A??
Brooke Clarke
brooke at pacific.net
Tue Apr 26 12:00:28 EDT 2005
Hi David:
How accurate is the pendulum clock now? How accurate do you want it to be?
Have Fun,
Brooke
Dr. David Kirkby wrote:
> The SRS is actually looking more and more attractive I must say,
> mainly because of its size (the Z3801A is not small), and the long
> holdover period if I can't get a GPS signal - which is quite likely.
>
> I'm tempted to take this in stages, using a reasonably large box,
> giving room for a number of items. My thoughts are:
>
> 1) Buy the SRS PRS10 and assume that is *right* for the purpose of the
> inital aim, which was to sync my pendulum clock. Errors in the
> rubidium source should be small.
>
> I'll leave the GPS initially - I have a lot of expenses at the minute.
>
> 2) Put some sealed lead acid batteries for backup - I suffer a lot of
> power failures at home. A friend has offered me a charger for 24V
> batteries.
>
> 3) Sync the pendulum clock to a crystal (either TCXO or perhaps an
> OCXO) - the latter being a bit over the top. This is going to be the
> hard part, especially as I will need a PIC to get 1 point something
> Hz, and I have not used PICs before.
>
> This will go in its own box.
>
> 5) Add an HP 10811A + Brooks Shera board to get low phase noise,
> syncing *not* to GPS, but to the PRS10. I have all the bits for the
> Brooks Shera board (apart from a few cheap ICs), so the cost in doing
> this is small.
>
> 6) Finally add a GPS, which should give me the low phase noise of the
> 10811A, with a decent holdover time from the PRS10 if there is no GPS
> signal.
>
> I suspect I could fit that lot (apart from 3 which I want sepparte) in
> a 3U rack.
>
> I'd need to synchonise the power-up of the two ovens as the power
> supply I have (24V, 2.4A) would not be capable of starting both ovens
> at the same time. The PRS10 take 2.2A on startup, but only 0.6A when
> running. Hence the 2.4A power supply should be okay in running both
> the PRS10 and the HP 10811A, but *not* starting them together.
>
> Any thoughts on that sort of idea above?
>
> Any obvious flaws?? Apart from the fact it is getting more and more
> expensive, and less and less related to the initial aim of making a
> couple of hundred year old pendulum clock more accurate!!!
>
> Dr. David Kirkby
>
> Brooke Clarke wrote:
>
>> Hi Tom:
>>
>> Don't forget that SRS has the free PC program Rbmon that talks to the
>> PRS10, although it's listed with a different Rb product.
>>
>> 73,
>>
>> Brooke
>>
>>
>> Tom Van Baak wrote:
>>
>>>> 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.)
>>>>
>>>
>>>
>>>
>>> The data sheet for the PRS10 is at:
>>> http://www.thinksrs.com/products/PRS10.htm
>>> http://www.thinksrs.com/downloads/PDFs/Manuals/PRS10m.pdf
>>>
>>>
>>>
>>>> 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.
>>>>
>>>
>>>
>>>
>>> The ADEV for a PRS10 at 1 to 10 seconds is on the
>>> order of 1e-11 making it 10x worse than the 10811
>>> inside a Z3801A. So the choice depends on what
>>> you want to use the output of your GPSDO for.
>>>
>>>
>>>
>>>> I guess a current unit is likely to be better than a 20-30 year old
>>>> one.
>>>>
>>>
>>>
>>>
>>> Not necessarily true. Some of the best oscillators in
>>> the world were made 30 to 40 years ago. On the other
>>> hand, you can't beat a PRS10 for features. Check out
>>> the manual for the list of commands.
>>>
>>> /tvb
>>>
>>>
>>>
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>>> time-nuts at febo.com
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>>>
>>>
>>>
>>>
>>>
>>
>
>
>
--
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w/o Java http://www.pacificsites.com/~brooke/PRC68COM.shtml
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