[time-nuts] HP5065 Frequency processing part II

[Ulrich Bangert]

David,

what you are saying, is it not more or less a patronage of my claim?

Because the factory selected resistors have surely be selected in a way
that tuning the frequency setpoint is possible in the sense

a) you have a fine enough tuning resolution to get the job done with
your fingers

and

b) the setpoint is always within the tuning range.

When the Ball-Efratom people decided to make the tuning range +/-10E-9
and used a 25 turn precision trimmer for that I understand it as an good
compromise between a) and b). If you have an single unit that has
changed more than 10E-9 over the years I would think that this one is
the outlier that is always possible. But in general they thought that
+/-10E-9 was more than needed over the lifetime.

Cheers
Ulrich Bangert

> -----Ursprüngliche Nachricht-----
> Von: time-nuts-bounces at febo.com 
> [mailto:time-nuts-bounces at febo.com] Im Auftrag von David Forbes
> Gesendet: Samstag, 11. November 2006 18:27
> An: Discussion of precise time and frequency measurement
> Betreff: Re: [time-nuts] HP5065 Frequency processing part II
> 
> 
> 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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