Hi,
On 05/05/2016 12:03 AM, Tom Van Baak wrote:
Hal,
How close could you get if you brought two of them together, compared phase,
drove them to the site for a nights work, drove them back to the same
location and compared the phase again.
That's essentially asking what the ADEV (or, TDEV) is for tau 1 day. Rb isn't
near good enough. Neither is Cs, for that matter.
Indeed. In this case the TDEV is of interest, as we have a 500 ps
requirement. Notice that TDEV is a RMS-type of measure and I think we
had the 500 ps given as a time error, you can't compare these values
directly, as the noise will have a different scaling factor depending on
the confidence interval around it that we want. The engineering factor
of 3 sigma would give us 99,7 % of the time it would be within those
limits, which may be good enough, this would mean that in normal
conditions I would divide my 500 ps with 3 to get the limit value.
The trouble is that we don't follow the normal gaussian noise and hence
error function but rather have the Chi-squared noise, so we need our
confidence factor from that. The principle is the same thought.
A bidirectional link should not be too hard to set up, and with some
care should be able to achieve this target.
Cheers,
Magnus
See www.leapsecond.com/tmp/5071a-12-run8-5d-10d.gif for a plot of a bunch of
5071A Cs clocks. They are compared together for 5 days to determine their
relative phase and frequency offsets and then go on a 5-day trip. You can see
how the phase drifts as random walk does its thing. It's way more than 500 ps
per day.
That's why the OP cannot use free-running clocks. He needs some method to
actively keep them in tight phase lock or passively compare them to within 500
ps in order to adjust the timestamps in post-facto.
/tvb
----- Original Message -----
From: "Hal Murray" <hmur...@megapathdsl.net>
To: "Tom Van Baak" <t...@leapsecond.com>; "Discussion of precise time and frequency
measurement" <time-nuts@febo.com>
Cc: <hmur...@megapathdsl.net>
Sent: Wednesday, May 04, 2016 10:30 AM
Subject: Re: [time-nuts] Fw: Optical transfer of time and frequency
t...@leapsecond.com said:
Any of these methods is going to be a challenge, given their 500 ps
requirement and their $2k budget.
How stable are surplus rubidium oscillators?
How close could you get if you brought two of them together, compared phase,
drove them to the site for a nights work, drove them back to the same
location and compared the phase again.
--
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