At 2:33 PM +0100 11/6/06, Ulrich Bangert wrote: >Hi Poul-Henning, > >> They don't have a "correct" frequency, only a very stable frequency. >> >> The actual resonance frequency of a rubidium standard depends >> amongst other things on the partial pressures inside the >> physics package. > >We are well aware of these facts! But if THAT were the reason to correct >for with different thumbwheel settings would not EVERY rubidium standard >in the world desperately need this kind of correction feature? > >Both my FRK-L and my LPRO need only C-field correction to get the >nominal 10.0000000 MHz out of it. Or has HP not been able to build the >physics packages more 'repeatable'? > >Cheers >Ulrich
Ulrich, We have a 13 year old rubidium standard at my place of work that drifted by about 1.5E-9 over its lifetime. This is within factory specifications, but beyond the range of the C-field adjustment trimpot. The rubidium vapor method does not generate anything like an exact frequency; it can vary quite a bit depending on the lamp, the gas, etc. The unit I was testing has a fixed resistor that is factory selected to set the C-field control in the middle of its range when the device is new. I could bring the C-field control back into range by changing that resistor if desired. That's apparently standard procedure for these devices. -- --David Forbes, Tucson, AZ http://www.cathodecorner.com/ _______________________________________________ time-nuts mailing list time-nuts@febo.com https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts