[time-nuts] New to Time Synching hardware - needing some advice

[Attila Kinali]

On Thu, 27 Dec 2012 10:19:46 -0800
Chris Albertson <albertson.chris at gmail.com> wrote:

> Yes you could us something like one of the low-cost rubidium
> oscilators to supply a pulse per second to Linux NTP and it would work
> for some time before the error was as large as 10 mS.
> 
> One missing requirement is how long you need be without GPS or
> networking.  Obviously you can't stay out of contact with the world
> forever but it is very easy and cheap if you only need a day. Harder
> if you need a month and expensive if you are talking about years.

Actually, a couple of months is still quite simple.
The Rb approace gives you at least something in the range of 10^-9 stability,
long term. Which gets you into the ballpark of 100 days (with 10ms). If you
temperature stabilize the Rb you should get down to 10^-11, which would
be 30 years. At least theoretically, aging is AFAIK larger than this.
But a couple of years should be still possible without too much effort.

IIRC the FE5680 sell now for 200USD. Some heatsink and temperature control
come maybe at 50-100USD. Some equipment to measure where the PPS lies
relative to UTC and a powersupply that can get you 15V from mains and
a battery (to get the Rb where the computer is) would also be necessary.

Alternatively, put the Rb next to the computer in question, hook a powerfull
linedriver to the PPS output, and a wire that goes all the way out where
you have GPS reception and can measure the PPS pulse. After measurement,
you can remove that cable.
Ofcourse this only works, if you can lay a cable temporarily. If you are in a
EMP secured room, the only way to get the pulse measured is the approach
with the traveling Rb.

			Attila Kinali

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