Fiber is not what I need because the system will not be in fixed
locations, and distances will be far more than 2km.
The requirements are to record photon arrival timestamps with a sampling
clock of 400MHz, 2.5ns resolution. The two clocks are independent, and
the timestamps will be the effective clock number at the photon arrival.
An averaging algorithm will be used to normalize the timestamps.
Since the software I'll use can adjust some "small" time drift. Some
clock cycle every houe is acceptable, so requirements, you see , are far
to be impossible.
1 clock cycle = 2.5ns
max clock cycles @ 1 hour = can vary, 1024 would be a good value.
Something achievable with commercial products and easily averagable by
software.
So:
1280ns each 1H dT (less is well accepted).
Ilia.
Il 29/04/2016 22:14, Magnus Danielson ha scritto:
Well, giving the conditions mentioned, doing ranging codes such as
those used by GPS is very easy and cheap. Doing this in bidirectional
isn't too hard. Doing a suitably high chip-rate should cost very little.
The two-way time-transfer is relatively easy, but you will need to do
some calibration to get the precision needed.
Now, what is the needed precision?
Why can't you pull fiber?
Still wonder how you use the time, to understand the timing requirements.
Cheers,
Magnus
On 04/29/2016 08:50 PM, Ilia Platone wrote:
There is line of sight.
The budget is around 2k€ by now, but can be increased.
This project is for an amateur astro club, and the resources they would
give to me are limited, except the place where to do this and some
optics.
The setup must be mobile, I mean that I should be able to place the
telescopes in other places "easily".
There is some material however. Material includes FPGA boards, VOCXO +
PLL boards, IR lasers and APD sensor boards, ARM boards, and consumer
PCs.
There is also the possibility to use some optics like small reflector
telescopes, as pointed before, they could be used as beam expanders for
IR lasers.
Ilia.
Il 29/04/2016 09:36, Michael Wouters ha scritto:
On Fri, Apr 29, 2016 at 1:18 PM, Bruce Griffiths
<[email protected]> wrote:
Quoting Michael Wouters: "According to this,
http://www.nist.gov/manuscript-publication-search.cfm?pub_id=912449
there are many practical challenges with a one way free-space
optical link."
That paper indicates that one way transfer with noise of a few
picosec should be feasible using an IR laser.
Oh, yes I see in Fig 2b that the short term, one-way noise is ca. +/-
5 ps. And probably with temperature measurements, the long term
variation could be compensated.
But we still don't know if there is line of sight.
Cheers
Michael
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Ilia Platone
via Ferrara 54
47841
Cattolica (RN), Italy
Cell +39 349 1075999
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