[time-nuts] Looking for good SR620 setup to compare GPS and rubidium

Brooke Clarke brooke at pacific.net
Thu Sep 7 16:46:54 EDT 2006


Hi David:

The most straight forward way is to make a time interval measurement 
between the two 1 PPS signals.
It's good to use a BNC-T connector at the SR620 front panel and a scope 
so that you can set the trigger levels at 50%.
If both sources are TTL (0 to 5 volts open circuit) and you use the 50 
Ohm termination in the SR620 then the pk-pk will be 2.5 volts and a 
trigger level of 1.25 volts works well.

By setting SAMPLE SIZE size to some number like 500 (seconds since your 
have 1 PPS input) you can then DISPLAY either MEAN or JITTER.
The latter is a very good indication of what's going on.

Have Fun,

Brooke Clarke

w/Java http://www.PRC68.com
w/o Java http://www.pacificsites.com/~brooke/PRC68COM.shtml
http://www.precisionclock.com



David Forbes wrote:

>Folks,
>
>We have a rubidium oscillator in a laboratory here that is ripe for 
>calibration against a primary standard. We have installed a Datum 9390 
>GPS receiver next to it as well as an SR620 counter.
>
>Can any of you recommend a good operating mode to make the SR620 reveal 
>the rubidium drift rate in a reasonably short time a couple days is OK) 
>so that we may adjust it to near zero?
>
>We have both 10 MHz and 1PPS available from both sources.
>
>We don't currently have a logging computer connected to the SR620, but 
>we can do that if needed.
>
>
>
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