[time-nuts] SE880 GPSDO

Mon Apr 25 20:50:54 EDT 2016

You've omitted the following pertinent data:
1) The idea is to correlate photon arrival times at pairs of stations with lateral separations of up to 1 km or so.
2) The Signal to noise ratio of the resultant measurement is proportional to    
    A) The geometric mean of the areas of the pair of telescopes          This cannot be too large as it smears out the details in the Fourier plane.   
    B) Square root of the electronic system bandwidth (or equivalently the reciprocal                of the photon relative arrival time stamp accuracy)  

    C) Square root of the observation time.
    The differential light path delays between the telescope pair can be up to 3.3us or so.
The effect of differential noise between the timestamps at a telescope pair is to in effect reduce the effective electronic bandwidth or equivalently increase the observation time for a given SNR. For example with a time stamp resolution of 1ns (~500 MHz bandwidth) the differential timestamp noise should be much less than this (ie 100-200ps or so). With a 10ns (~50MHz bandwidth) timestamp resolution 1-2ns of differential timmestmp noise is tolerable, however the required observation time increases by a factor of 10 for a given SNR.
The SNR is independent of the optical filter bandwidth so that with a sufficiently narrow optical filter bandwidth its possible to ensure that photon counting is feasible.

The original Hanbury-Brown Twiss interferometer used 10m light buckets running on a circular railway track with interconnecting coax cables. The position of the collector pair was adjusted to maintain the baseline at right angles to the light path to the observed object thus ensuring zero differential light path delay between the collectors. The two signals were multiplied together using an analog circuit with a bandwidth of around 40MHz. Observation times of several hours were required even for relatively bright stars.
 For further details see:Long baseline optical intensity Interferometry

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| [1506.05804] Long-baseline optical intensity interferome...Submission historyFrom: Dainis Dravins [view email] [v1] Thu, 18 Jun 2015 20:00:34 GMT (4473kb,D)  |
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Bruce

    On Tuesday, 26 April 2016 11:03 AM, Bruce Griffiths <bruce.griffiths at xtra.co.nz> wrote:

 There's no spec for th 10MHz option you originally specified.What's the jitter bandwidth of interest?

Still need a spec for the data logging system timebase error.This is for your intensity interferometer?

Bruce 

    On Tuesday, 26 April 2016 10:00 AM, Ilia Platone <info at iliaplatone.com> wrote:

 I haven't bought anything yet, so feel free to recommend me any 
components/setup.

here is the datasheet I am referring to: 
http://www.foxonline.com/pdfs/FVXO_HC53.pdf

It contains some informations about phase jitter on page 5.

The

I selected this because of the CMOS output, since I didn't find any 
Connor Winfield osc with these levels yet.

Actually  want to achieve less than around 78ps jitter at 125MHz. (this 
should be achievable using this also: 
http://www.digikey.it/product-detail/it/fox-electronics/FVXO-HC53B-125/FVXO-HC53B-125-ND/2153894)

Let me know,

Ilia.

Il 25/04/2016 22:51, Bruce Griffiths ha scritto:
> On Monday, April 25, 2016 09:41:57 PM Ilia Platone wrote:
>> Hi all,
>>
>> I'm trying to build a GPSDO with a FVXO-HC53BR-10 (Fox Electronics) VCXO
>> and a Telit Jupiter
>> <http://www.digikey.com/Suppliers/it/Fox-Electronics.page?lang=en>SE880<http
>> ://www.digikey.com/Suppliers/it/Fox-Electronics.page?lang=en>, this serves
>> for a datalogger an I want to achieve a highly reliable clock.
>>
>> This GPS receiver has two clock inputs: a 16MHz, and a 32KHz XT input
>> for the RTC functions.
>> My problem is this: The crystal must be driven by a voltage depending to
>> the phase difference between the GPS 1PPS output and the uC 1s cycles,
>> but must I drive (feedback) the RTC of the GPS also from a divider of
>> the main clock, or the 16MHz TCXO input, or both (or none...)?
>>
>> Suggestions of any other component, for driving both the VCXO, and
>> possibly for a RTK implementation, are welcome.
>> Thank you,
>> Ilia.
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> What are the timing specifications for the data logging system?
> Without this data, its not possible to decide if the proposed GPSDO will meet
> these specifications.
> Whist its possible to construct a GPSDO using almost any crystal controlled
> oscillator, the timing performance will vary widely.
> The datasheet for the Fox VCXO you selected does not specify the phasenoise,
> jitter or ADEV for the 10MHZ option.
>
> Bruce
>  
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