[time-nuts] HP5065 Frequency processing part II

David Forbes dforbes at dakotacom.net
Sat Nov 11 12:26:47 EST 2006


At 6:03 PM +0100 11/11/06, Ulrich Bangert wrote:
>Hi folks,
>
>If you look at the schematics of a Ball-Efratom FRK-L rubidium standard
>you will notice that it has a fixed frequency synthesizer stage to
>generate the microwave frequency from the 10 MHz OCXO. There is NO
>possibility to tune anything concerning the microwave frequency of the
>physics package OTHER than the C-field setting. Since the C-field
>setting covers a frequency range of +/- 1E-9 relative this seems to be a
>strong indication that all efects that you decribe (including a exchange
>of the physics package) must be WELL below 10E-9 relative. With the
>resonance frequency in the 7 GHz region +/-10E-9 makes abt. +/- 7 Hz
>absolute. Note that this +/-7 Hz matches pretty much the way how the
>rubidium's frequency is usually specified as x.xxxxxx +/- 4 (7)Hz for
>example on TVB's pages. Up to this point I am in harmony with the world.

Ulrich,

The limits of rubidium oscillator operating range is larger than you 
have calculated.

The unit I was trying to adjust had drifted outside the range of the 
C-field adjustment control. This drift occurred over 13 years of use 
in a laboratory environment. It was a total of approximately 1.5E-9 
drift.

The thing that can be changed to accommodate this drift is the 
factory selected resistors in the C-field setting control circuit. 
See R10 and R11 on board 3, the 20V supply board.

I don't know what the maximum variability range is, but if it was 
less than 1E-9 then these resistors would not be factory selected.
-- 

--David Forbes, Tucson, AZ
http://www.cathodecorner.com/




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