On 01/19/2011 04:17 PM, Brooke Clarke wrote:
Hi:
Here's a response I got from Symmetricom:
· The SA.45s actually uses cesium, not rubidium. But it is a vapor-cell
clock just like our Rb clocks.
Which is apparent from papers published over time.
· The Tx and Rx pins are for an RS-232 interface. Using the interface,
the clock can be programmed, and the clock’s functions can be monitored.
I have attached a User’s Guide that describes all the commands in detail.
It's didn't make it through. Toss it my way and I toss it on the web.
· The SA.45s does not attempt to correct the 1 PPS input, nor does it
use a sawtooth to correct itself to the 1 PPS input. Instead, it can be
commanded (see User’s Guide) to discipline itself to the 1 PPS input.
How fast it does this is a function of user-selected bandwidth inputs.
Slap a GPS receiver on top of it and a small micro-controller to
interface to them both and you have one compact solution and really nice
hold-over properties for its size and power.
I get the feeling that a vapor cell is not an absolute standard but
rather works like a Rb vapor cell, i.e. the frequency has some drift and
the starting frequency depends on how the cell was made.
You *will* have wall-pulling effects, to some degree compensated by the
buffer gas and also the laser amplitude will cause a pulling effect.
This is a secondary standard and not a primary standard. Compare it up
against telecom rubidiums for a more suitable size, power and
performance matchup. This is not to discredit it, but rather put it in
the right context.
The 1 PPS output can be synchronized (using the 1 PPS input) to the
nearest 10 MHz zero crossing (i.e. to within 50 ns). With a continuously
applied 1 PPS input after some time it will adjust both the frequency
and 1 PPS output to about 5E-13.
Not bad.
Cheers,
Magnus
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