[time-nuts] Pressure sensitivity of Rb vapor cell standards

[ew]

Juerg and I have a few FRK and M100 along with spare bulbs to cover our remaining life. We have done extensive testing and learned a lot. We for instance have experimented with loop time constant 0.1 to 20 seconds and have found out that the best AV is with 1 second. We also did consider using Laser Diode to improve AV. My idea was to buy some diodes that cover the spectrum and have a friend in Hergiswil that has the optical plug in for the HP 70 000 series spectrum analyzer characterize and select candidates. Worked with Corby on proper optics. Assemble a unit feed a precise frequency in to the unit from an external source and use the loop filter to control the C Field. Monitor and adjust the Diode. Once the unit shows stability use a PIC ADC input to monitor the filter output and with a 1655 control the Diode. The time constant would be longer than the 1 second for the OCXO. Now that we both have HP5065A's with according to Corby some of the best AV there is no motivation at this age to pursue this venue. To many other projects on our plate. Also think an optical filter should be reconsidered, Corby did some tests but forgot to change the time constant. I have presently 4 units running to find the best long term aging for my Maser replacement project. See no change at 1 E-12 changing voltage from 22 to 24 V. Slight change while changing but back to same frequency after 20 seconds. Also no change 1 E-12 with 2.7 C ambient change. Presently no fan control. Aging test will be done with 1 E-14 resolution. After 3 month of aging test the two best will get fan control for additional tests. Goal is to control a Rb in 24 1E-15 steps per day. Ambient pressure is also part of the control loop. A OSA 8607 will be the clean up.