[time-nuts] SE880 GPSDO

Bruce Griffiths bruce.griffiths at xtra.co.nz
Wed Apr 27 04:12:20 EDT 2016


A 60kHz receiver is unlikely to be useful for nanosecond timing applications.
Bruce
 

    On Wednesday, 27 April 2016 6:36 PM, Ilia Platone <info at iliaplatone.com> wrote:
 

 Hi All,

I read from an article about this receiver: C-Max CMMR-6P-60

Can it be useful?

One of the places where I'll setup the telescopes will be in mount 
Carpegna, near where I live. There are the repetitors of television and 
radio over there. Can the carrier wave of such repetitors be used as 
clock? they will be distant 5 Km or less from the observation location.

Regards,

Ilia.


Il 26/04/2016 23:51, Attila Kinali ha scritto:
> On Wed, 27 Apr 2016 08:25:55 +1200
> Bruce Griffiths <bruce.griffiths at xtra.co.nz> wrote:
>
>> 1) Relative position of any pair of clocks located up to 2km apart has to be
>> known to within 3cm or so. Post processing is OK, however differential Earth
>> tides between the clock locations may need to be considered.
> That's doable. People at ETHZ got sub cm accuracy from LEA-6T modules
> with post-processing of the recorded phase data with an integration time
> of several hours. Using phase data of multiple timing modules should give
> relative positions with better than 1cm accuracy on these short baselines..
> I don't know how much post-processing is necessary though. Haven't looked
> into the the field of RTK[1] and PPP[2] yet. Probably data from IGS[3] is
> needed as well.
>
>> 2) The difference in the time offset between any pair of clocks located up to
>> 2km apart shall not vary by more than 200ps (1ns time stamp quantisation) or
>> 2ns (10ns timestamp quantisation) over an 8 hour period (at night).
>> Post processing of data to fit wander etc is not practical as the SNR is too
>> low to support this.
> Now this is quite a bit more challenging. While i'd say 1ns should be doable
> (using receivers that are calibrated against each other and using common in
> view mode during post-processing of the data), i'm not so sure whether 200ps
> is possible. What might work is using an LEA-M8F with it's external frequency
> input, to record the phase of an stable external reference (e.g. Rb).
> Averaging that over a dozen minutes or so should make it possible to
> measure the phase of the reference oscillator with 200ps precision, relative
> to the other stations.
>
> Another way would be to use L1/L2 receivers with calibrated antennas.
> I know that BIPM has a GPS station that can deliver time transfer
> accuracy <2ns over a distance of several 100km. It could be possible
> to use such receivers with the <3km distances to deliver 10 times better,
> if they are frequently calibrated (eg. every couple of days).
> But of course, this makes things much more expensive.
>
> But all this is a wild guess. I haven't seen anything like this done.
> If you want a more precise answer i would need to think about the design
> of the system for some time.
>
>
> I guess using some cable/fibre between the telescopes is out of question?
>
>
>             Attila Kinali
>
> [1] http://www.navipedia.net/index.php/Real_Time_Kinematics
> [2] http://www.navipedia.net/index.php/Precise_Point_Positioning
> [3] http://www.igs.org/
>

-- 
Ilia Platone
via Ferrara 54
47841
Cattolica (RN), Italy
Cell +39 349 1075999

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