[time-nuts] LPRO-101 with Brooks Shera's GPS locking circuit

Dr Bruce Griffiths bruce.griffiths at xtra.co.nz
Tue Dec 19 17:24:42 EST 2006

Magnus Danielson wrote:
> From: Brooke Clarke <brooke at pacific.net>
> Subject: Re: [time-nuts] LPRO-101 with Brooks Shera's GPS locking circuit
> Date: Tue, 19 Dec 2006 13:42:28 -0800
> Message-ID: <45885CC4.30007 at pacific.net>
>> Hi Brendan:
>> It's interesting that the PRS10 can time stamp the 1 PPS input with a 
>> resolution of 10 ns.  I wonder how they do that.
>> http://www.thinksrs.com/downloads/PDFs/Catalog/PRS10c.pdf
> It actually says it does it with 1 ns resolution. A x100 analog interpolator
> circuit for 1 ns to 100 ns (10 MHz) isn't rocket science. See the HP 5335A
> operations and service manual. Getting 10 ns accuracy isn't supprising.
>> When I picked up my PRS10 at the factory during the tour I learned that 
>> the 10 MHz oscillator in the PRS10 was an improved version of the SC10.  
>> There's an Allan plot for the PRS10 at:
>> http://www.thinksrs.com/products/PRS10.htm <- overall PRS10 page
>> http://www.thinksrs.com/assets/instr/PRS10/PRS10diag2.htm  <- Just the plot
> Do the PRS10 comes with the 5 dollar tour ticket or is it the other way around?
> :D
> The PRS10 seems like a good device.
> Cheers,
> Magnus
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The PRS10 is somewhat marginal for VLBI although it has been used for 
short integration times to observe the L band hydroxyl line at around 
1600 MHz.
Fortunately all stations but one used hydrogen maser clocks/frequency 
standards. Some of the better crystal oscillators (Oscilloquartz 8607 
BVA, FTS1200 etc) have better performance for integration times up to 
100s or so. The PRS10 OCXO DAC has a fractional frequency resolution of 
around 1E-12. This limits its performance for VLBI with long integration 
times where it is necessary to have phase synchronisation between all 
stations to within 10 degrees or so over the integration time.


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