[time-nuts] Got 60HZ?

[Javier Herrero]

I'm sure that the spectral purity that you obtain by first multiplying 
and then integer dividing is far better that using any fractional 
division, moreover if you are not multiplying by a big number :)And not 
need to use too much weird circuitry if you use as I mention a 
microcontroller that integrates it along with a programmable timer that 
can be used to divide it. Also, the jitter and noise from the PLL 
multiplication is reduced by the division (the resulting 60Hz would not 
be so bad, believe me - I've use a similar technique for generating 
square or PWM-modulated signals in the kHz range. In that cases jitter 
were not an important parameter so I did not measured it, but the 
resulting signals were quite clean).

Cs sources are rare and expensive, and Rb sources are more common, 
mainly due to the price and size of the physics package. The Rb lamp is 
a quite simple and small device, but a Cs tube is rather more complex, 
big and difficult to manufacture. Although this could change in the 
future - there has been several publications (reflected on this forum) 
about micro-miniature Cs sources.

Best regards,

Javier

El 11/12/2010 07:11, Michael Poulos escribió:
> Javier Herrero wrote:
>> It seems that we're all trying to find the most obstuse way to obtain 
>> 60Hz from 10MHz since the division is not integer... why not simply 
>> multiply the 10MHz input signal by 3 and feed the resulting 30MHz 
>> signal to any suitable divider by 500000 chain? the result will be 
>> nice, spectrally pure and even 50.000% duty cycle :).
> To multiply the frequency means weird RF circuitry to start off. If 
> you start off with the 10 million HZ and divide, you only get better 
> as any phase jitter gets lost in the division. As you divide far 
> enough, the phase jitter gets to those "leap pulse" jitters. To design 
> around the problem of Rb (my bad about Rb versus Ru) movements you 
> have to have a second one ready to start once the original goes bad. 
> This will occur with a cesium movement, like a good Agilent 5071A 
> cesium movement every bit as well A fun question is why Rb movements 
> are so common but Cs movements are rare and expensive.
>
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Javier Herrero                            EMAIL: jherrero at hvsistemas.com
Chief Technology Officer
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