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

[Brooke Clarke]

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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>>>
>>>
>>>
>>>  
>>>
>>
>
>
>

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