[time-nuts] distirbuted sync

[Jim Lux]

Starting a new thread...

Brian wrote:
Have you considered WWVB?  Works fine within structures.
Even though the carrier today is phase modulated one can probably glean 
1 ms accuracy from it or the data transmitted.

-- disasters occur world wide, any time day or night, so depending on 
WWVB won't work.

Magnus wrote:

The movie-business have similar problems, so a sync-ones and keep drift 
low system emerged to make field recordings easier.

If it would be tolerable to have a "central" transmitter, putting a PN 
code over a voice radio system would suffice to keep the drift fairly 
well kept together for this form of system. If you choose to do it on 
the audio channel, then you can use of the shelf radios, and replace 
those or re-program those as needed. Also, they are dirt cheap nowdays.

-- yes, I'd thought about that, but that's another piece of gear (the 
centralized transmitter).  And if we added another radio into the 
system, you get into the whole size, weight, power aspect.  We already 
have to have the GPS (for those places where GPS is available).  We 
already have a comm link of some sort (TBD.. long range Bluetooth 
possibly) between the modules, so we could transmit a sync signal on 
that.  The question would then be whether *that signal* has modulation 
and propagation characteristics that allow the frequency disciplining. 
BT is 2.45 GHz, and subject to all the multipath and other ills we 
encounter with the radar at 3 GHz.

This is a bit down the road a bit, so what might wind up being the 
ticket for GPS denied is putting up GPS pseudolites at the site.  that's 
back to the "extra piece of gear" problem, but maybe we could make a 
case that it isn't *our* piece of gear<grin>.

Or have our modules have the ability to transmit a GPS-like signal that 
the GPS-18 would appropriately handle  (oh yeah, I can see the 
regulatory issues looming for that one!)

It *is* an interesting problem.. It's sort of weird, though, as I write 
the requirements..

High frequency accuracy (1E-10, 1E-11) ideally.. or high stabiity over 
1-100 seconds, with a way to get "knowledge".

But relatively low timing accuracy: 1-3 milliseconds over the same 100 
second interval (1E-5)

Often you have a time requirement that is commensurate with the 
frequency requirement.