Hi David:
There's an appendix in the Stanford Research manual for the PRS10 Rb oscillator that explains how to make 1,000 measurements each second and thus get 1 ps accuracy every second. It involves using a precision external clock into the SR620 and connecting the Ref Out (1 kHz derived from the internal or Ref oscillator) into the External Gate input. The Start and Stop signals need to be something like 10 MHz, or probably any frequency at or above 1 kHz. And the gate is used to enable a measurement 1,000 times per second.
Each second you could see a drift of 1E-12 and 1E-14 in 10 seconds! I'm going to try using this method to set one Cs standard to the one I think is now set.
Note that some of the HP counters can display a large number of digits per second when measuring frequency, BUT NOT in time interval mode.
I think the 5370A or 5370B can, but without a manual, or an instrument to play with, I really can't say. But I have an instrument on order, and will search for a manual once I know the S/N, as I gather it is critical to get the right manual.
I like the SR620!
There's one on eBay now
http://cgi.ebay.com/ws/eBayISAPI.dll?ViewItem&category=25401&item=7507651064&rd=1&ssPageName=WDVW
but the starting price is 5x more than I paid for the 5370B.
I like Stanford kit. Have several of their lock-in amps at work. I think we have more usable lockins than scopes!!
-- Dr. David Kirkby, G8WRB
Please check out http://www.g8wrb.org/ of if you live in Essex http://www.southminster-branch-line.org.uk/
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