Hi Bob:
It was my understanding that the receiving station knows the path taken, is that the case? Or are you saying even when
it's the same path the time delay has large variations?
Have Fun,
Brooke Clarke
http://www.PRC68.com
http://www.end2partygovernment.com/Brooke4Congress.html
Bob Camp wrote:
Hi
Since the network is being measured, I suspect that using it as the time
reference would present a basic problem.
Bob
On Feb 20, 2012, at 2:07 PM, Jim Lux<[email protected]> wrote:
On 2/20/12 10:31 AM, Bob Camp wrote:
Hi
Simple answer:
A rack mount cesium standard is as good as you can get. Figure on 15 ns per day of
drift. That gets you to 15 us in 1000 days. You may or may not get one that drifts
that little, a lot depends on little details. For> 3 years, consider an
ensemble of cesiums. At $50K each cost can go up pretty fast.
There is nothing out there that will do better stand alone for less money.
Either you get a sky view or you change the budget....
Bob
But he *does* have the ability to have an external network connection.. So the
real question is whether one could come up with a better-than-NTP scheme to get
the 100 (or 10) microseconds.
I suspect that with sufficiently controlled network paths (which might be
doable in a widescale deployment) and a tweaking of the NTP stuff, you might be
able to get it to work.
100 microseconds out of a day is 1E-10, which is actually a fairly liberal
drift spec for an OCXO or even a TCXO. (which are things like ppb/day)
Maybe there's a particular time of day (or day of week) when network uncertainties are
minimal, or can be bounded. So what you really need is a onboard oscillator that is good
at "carry over" between periodic calibration checks.
One question about the 100 microsecond spec.. is that a worst case at any
instant, or is it an average spec over a day (so a consistent diurnal variation
would cancel out)
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