[time-nuts] Rubidium aging

[ew]

When it comes to aging of Rb's I can look back at 30 years of first hand experience. Most my work has been with FRK and M100. Juerg joined me 7 years ago. Now both of us have HP5065A's that Corby worked over and according to him are two of the very best he has seen. Data will be shared soon. We are now  in the process of characterizing long term behavior.

Long term aging on FRK and M100 is typically less than 2 E-12 per month on our better devices.

It is also important to recognize that all our work is limited to a 15 to 35 C environment. This is not the commercial world. 

In 1971 I bought in TI a Tracor 599 Omega receiver and converted it to 60KHz. TI liked it and asked me to convert a total of 15 units including global frequencies and loaned me a Sulzer OCXO.  At the time all has HP 5065A and some HP 5061A. At completion they let me have the leftovers for $100 for all and $ 100 for the Sulzer. I did not know it then but I became a time nut.

In 1985 I bought a new FRK L, I think it was about $ 3000. Added Fan temperature control and in 1994 having moved to Miami added aging control using a 12 bit blue Phibrik DAC. Stepped every 3 hours driven by a Collins 3 MHZ TCXO. Fine tuned the TCXO against the Tracor. Once a year reset the DAC using one of the Fluke DC Voltmeters with the multi 10 step dials. Remember those. Only way to measure precise frequency was the Tracor.

When I bought the first Austron Loran C/2110 the FRK was in the E-13 range. FRK  died after 26 years, black lamp and Tracor does not work with the new 60 KHz signal.

But I learned and am convinced that aging control along with temperature and pressure compensation will give us performance at least as good as a passive Maser. Will use a 10 MHz TCXO or OCXO along with a 16 bit 1655 DAC  in 1E-14 steps or better. The PIC that controls the DAC will also be able to swallow a pulse if we want to include GPS update. But GPS correction will be limited to once a week. Will be tested.

Close in clean up will be OSA 8600 and 8607.

I will focus on FRK because of past experience and I do not trust my eyes to mess with the HP5065A but it will come in handy during tests.
Bert Kehren 
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