[time-nuts] Smart fiber-optic cable ( a reference to Hp's smart clock )

Jim Lux jimlux at earthlink.net
Mon Feb 4 22:37:57 UTC 2013


On 2/4/13 2:09 PM, Stanley wrote:
> If a fiber-optic cable had temperature sensors either installed with or embedded inside of this could make for better modeling changes in delay making more accurate transfer of time and frequency possible. With fiber to tower installs now under way to provide more data at cell towers why not backup GPS frequency and time transfer with the same medium ? Would this also increase the data rate of the cable ? That is faster rates due to the better timing uncertainty.
>

ACtually, you could *measure* the delay in the cable by sending a signal 
down it and then sending it back on another fiber in the same bundle.

I suspect, though, that this strategy would be more expensive than a 
$1000 GPS disciplined OCXO or something.

Setting up a scheme to measure the prop delay (or temp) might be fairly 
expensive, when the GPS strategy is pretty inexpensive and reliable.

That said, radio astronomers and the Deep Space Network do measure fiber 
temperatures and stuff, but those guys and gals are obsessive about 
measuring everything to a fraction of a gnat's eyelash. (and 
compensating for the CTE of the gnat).

  For another thing, I'll bet the same entity doesn't own the cell site, 
the equipment, the fiber, and the other end.  That is, if you're ACME 
cell company, you basically buy a "data connection" at your cellsite, 
and someone else worries about how those bits get to the other end. 
There's some service level agreement that specifies error rates and 
availability.   I don't know, though.  They may just rent dark fiber.




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