[time-nuts] GPS discipline oscillator vs phase lock
kb8tq at n1k.org
Fri Jun 16 18:29:31 EDT 2017
> On Jun 16, 2017, at 6:21 PM, Attila Kinali <attila at kinali.ch> wrote:
> On Fri, 16 Jun 2017 17:46:45 -0400
> Bob kb8tq <kb8tq at n1k.org> wrote:
>> A far more common approach is to let the two oscillators free run and to
>> record something like a local broadcast station.
>> You then post process all of the data to give you the phase accuracy. One of
>> several gotcha’s is the stability of any
>> radio link at the level you are looking for.
> Well, we still don't know what the requirements are.
…. well, we do. A requirement of 0.1 degree at 100 MHz was stated earlier on.
That’s where the ps stuff comes in.
> Though I doubt that a GPSDO cannot deliver the needed stability.
> Unless the goal is to build a multi-static radar that can locate
> a plane down to sub-cm range, ps level stabilty is not required.
> Even something as demanding as VLBI is in the couple ns range.
> (But they measure over long intervals (hours) which puts higher
> demands on the local oscillator)
> Another reference value: Time transfer using calibrated GPS receivers
> achieves an absolute accuracy of about 1-2ns(RMS) over base lines of
> several 10km with single frequency receivers. Dual frequency receivers
> have been reported to do <200ps over 400km (TDEV <60ps up to 5days).
> Attila Kinali
>  "Comparing a GPS time link calibration with an optical fibre
> self-calibration with 200ps accuracy", by Jlang et al 2015
> You know, the very powerful and the very stupid have one thing in common.
> They don't alters their views to fit the facts, they alter the facts to
> fit the views, which can be uncomfortable if you happen to be one of the
> facts that needs altering. -- The Doctor
> time-nuts mailing list -- time-nuts at febo.com
> To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts
> and follow the instructions there.
More information about the time-nuts