[time-nuts] Rubidium stability

Joe McElvenney ximac at btinternet.com
Sun Apr 29 15:23:56 EDT 2007


>Is this variability more likely due to the rubidium source (failing bulb) or
>due to problems with the 5334B counter?

   Obviously you need a third source for comparison while locking
your counter to the Rb source.

   I gather from the web that the Lucent unit uses an Efratom
module in which case there should be a lamp voltage display or at
least a measurement pin for it available somewhere. I posted an
old Efratom FRK manual to BAMA some time ago which may give you a

   A good lamp will show better than 5V although this is actually
the voltage on the output of the photo-detector amp. New lamps are
available on the web although I replaced mine in a Racal 9475 Rb
standard some time ago with no obvious improvement; it still reads
5.8V when the manual says it should be between 6 and 12V. I was
told once that varnish can slowly evaporate onto the cell window
thus reducing optical transparency. Don't know if this is true but
it is a thought.

   Cheers - Joe G3LLV

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