[time-nuts] 1 pps Accuracy in two locations

[Mike Ingle]

Hi Martyn,

I think a few 10s of ps 1sigma error on the 1pps output should be
achievable.   If for example the Rb was free running, and had for example a
100MHz (instead of 10MHz) output, it is not too difficult to measure the
PPS arrival time of the GNSS PPS down a 10ps uncertainty relative to the Rb
reference.  Doing this over a long interval, and fitting the history,one
should be able to predict when relative to the Rb oscillator the next PPS
should occur. This would be in the form of a clock cycle number and
fraction.  Then you should be able to create the PPS output by delaying the
appropriate cycle by the fraction.  One method would be by using a DAC to
control the threshold of something like the ADCMP-580  and creating a ramp
on the other input.  I am 100% certain of the possibility of measuring to
10ps or less, but only theorize the delayed output can be produced,  There
are also delay vernier chips, but I am not familiar off the top of my head.

--mike

On Wed, Dec 4, 2019 at 3:41 PM <martyn at ptsyst.com> wrote:

> Hello,
>
>
>
> I'm always being asked to provide equipment that can produce two 1 pps
> outputs aligned to each other to within a few ps.
>
>
>
> These two 1 pps pulses are not in the same location and could be 100 metres
> to a few km away.
>
>
>
> So they are asking for two of my GNSS frequency standards with 1 pps
> outputs.
>
>
>
> The 1 pps outputs being derived from the rubidium oscillator (which is
> aligned to GPS/GNSS)
>
>
>
> The best I think I can achieve is in the low ns range.
>
>
>
> Does anyone know how this can be achieved?
>
>
>
> Regards
>
>
>
> Martyn
>
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