Thanks Bruce,
I know this, the delays due to the light path difference will be
calculated later by software, and i can have filters with a bandwidth of
3-5 nm, two 0.4m diameter telescopes. the distance of the two telescopes
will be around 2500m and the maximum delay between these two signals may
be 8us. The expected photon flux (the actual center frequency of the
data logged) will be less than 10M/s, but the clocks that record these
data must be synced with a maximum error of some ps, otherwise I'll not
find any correlation.
I would propose a software capable of aligning these two (or more,
sequentially) logs by finding correlation by a slighty variable
time-base, excluding pseudo-correlations by a discriminating algorithm,
but this is for an interferometry forum/list maybe.
Regards,
Ilia.
Il 26/04/2016 02:50, Bruce Griffiths ha scritto:
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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| View on arxiv.org | Preview by Yahoo |
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Bruce
On Tuesday, 26 April 2016 11:03 AM, Bruce Griffiths
<[email protected]> 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 <[email protected]>
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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--
Ilia Platone
via Ferrara 54
47841
Cattolica (RN), Italy
Cell +39 349 1075999
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