[time-nuts] GPSDO and oscillator steering - EFC vs DDS schemes?

Attila Kinali attila at kinali.ch
Wed Dec 9 05:47:58 EST 2015


God eftermiddag,

On Tue, 8 Dec 2015 23:45:52 +0100
Magnus Danielson <magnus at rubidium.dyndns.org> wrote:

 
> If you would setup essentially a micro-stepper design, such as those 
> being used for cesium and hydrogen masers, but maybe adapted to a 
> hobbyist needs and with straight-forward way of building and tune-up, 
> then we could alter the design pattern. The phase-noise and long term 
> stability issues is clear.

It doesn't look too difficult to crank something out within a rainy
weekend or two. But I am most likely underestimating the amount of work :-)
 
> Doing control loop using a phase-stepper is a little bit different, and 
> has a few minor design-challenges, but once mastered is essentially the 
> same. EFC or C-field control then becomes more an initial setup.

What makes the control loop different (beside that you control phase
and not frequency, and thus have to integrate)?


> An alternative approach divider wise is to use re-generative dividers.
> For Rick's approach there would be a number of these at the same 
> frequency (nominally), so the same design-pattern would apply. However, 
> that would only be meaningful if you need really need to keep the noise 
> down.

Yes, I thought about that as well, the problem here is that the low
noise mixers designs use transformers, which make everything bulky
and expensive (the usual suspects cost 2USD/piece and use about 1cm^2).
The one design that comes to mind that doesn't need transformers is
the tripple Gilbert-Cell design, but that might be higher in noise.
(Heck, i should just sit down and do some noise calculations)
Additionally, there is a need for relative steep filters for 667kHz


			Attila Kinali


-- 
It is upon moral qualities that a society is ultimately founded. All 
the prosperity and technological sophistication in the world is of no 
use without that foundation.
                 -- Miss Matheson, The Diamond Age, Neil Stephenson


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