[time-nuts] Antique Rb Standard - Thanks, Pictures, Parts Request, Question

[paul swed]

I will strongly agree about the cavity and not tuning it. The key is the
multiplication chain and unless the srd is bad the rest of the chains
pretty reasonable in the frequencies used.
Typically a fair amount of power just before the srd.
Regards
paul.

On Sun, Apr 29, 2012 at 4:19 PM, ed breya <eb at telight.com> wrote:

> If the Rb cell "drifted" enough (maybe if it was filled with water) to
> de-tune the mechanical cavity resonator, it wouldn't work at all. Only a
> small amount of the RF power in the cavity is coupled into the Rb gas. The
> bandwidth of the Rb resonance is a fraction of a Hz (Q in the millions),
> while the bandwidth of the cavity is probably 20-50 MHz, (Q may be up to
> 100).
>
> The multiplier will multiply frequency by integers at each stage, but each
> stage is tuned to maximize its response at the desired harmonic. You have a
> chain of these, each needing to be peaked to get the net result - enough
> power at the right frequency to drive the SRD. Then the SRD has to be
> optimally biased to maximize its power output at the desired harmonic. Then
> the cavity has to prefer that particular (98th or whichever) spur - but it
> isn't an extremely narrow filter - it can't be since it's just a single
> section. It has to be good enough to "reasonably" attenuate the nearby
> spurs spaced at around 69 MHz away, and to be the tuned load for the SRD to
> maximize the power at the desired frequency.
>
> So, the guts need to provide the cascade of discrete frequencies that
> ultimately lands one near the Rb resonance in order to detect it, but each
> stage and each part has to be right for it to work. The Rb resonance is by
> far the most stable of all of the parts of the system - even after 40 years
> or any number of years.
>
>
> Ed
>
>
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