[time-nuts] SE880 GPSDO

Ilia Platone info at iliaplatone.com
Wed Apr 27 05:23:39 EDT 2016


It was a joke :)

Interesting the idea of Attila, it can be the less expensive solution:

"Assuming that you have an amateur radio license, you could use a
well located central station to transmit a CW signal in the 70cm or
23cm band. There should be some effort put into this station
to make it stable (eg by using a good rubidium as frequency source,
or even an ensemble) and low noise."

...

"Now that all stations have the "same" frequency, one can use the GPS
module to get the time information using long integration times.
Under the assumption that the (sawtooth corrected) PPS is good to ±10ns
an has a nice, time-invariant distribution, it should be possible to get
below 1ns in precision within 100s. Using common view phase data it
should be possible to get even better than that."

Regards,
Ilia.

Il 27/04/2016 10:12, Bruce Griffiths ha scritto:
> 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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