Ralph Smith wrote:
On Thu, September 9, 2010 1:10 pm, Matthew Kaufman wrote:
On 9/9/2010 8:37 AM, Ralph Smith wrote:
We have a requirement for approximately ten radio sites to be
synchronized
to within 30 ns of each other.
30 ns seems a little closer than most radio site applications need...
what drives this requirement?
Aircraft surveillance using multilateration.
and presumably some form of bistatic radar with an illuminator and
multiple receviers isn't going to cut it?
You're fairly close.. is any RF method out of bounds? Could you radiate
a low frequency signal that propagates by ground wave?
(e.g. Omega.. but I don't think it was anywhere near nanoseconds..)
Even a really, really good ovenized quartz oscillator isn't going to be
that good. You're looking for 1E-13 sorts of precision, right (50 ns
out of 500,000 seconds). I seem to recall numbers like 1 part in 1E10
over 400 days. You might do better with selected units, but this is
million dollar a copy sort of units. The Cassini USO drifts between
1E-12 and 1E-11 per day.
You're really looking at Cs standards... (about 2E-14 at 1E6 seconds)
Ordinarily you could throw in an
appropriate GPSDO and be done with it. However, we also have the
reqirement to be able to operate independent of GPS for up to six days.
Wow, ok, and what drives *that* requirement? Can you use any other
Paranoia. People making the requirements are concerned with GPS going away
due to solar flare or some other reason.
mutually visible thing, or do we assume all satellites have vanished
from orbit?
No satellites.
Thanks,
Ralph
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