[time-nuts] cheap 5V OCXO in 14DIP has about 1E-9 drift per day

Magnus Danielson magnus at rubidium.dyndns.org
Sun Apr 17 10:16:47 UTC 2011


On 04/16/2011 10:50 PM, Bruce Griffiths wrote:
> Bruce Griffiths wrote:
>> Oz-in-DFW wrote:
>>>
>>> On 4/9/2011 11:29 AM, Greg Broburg wrote:
>>>> <deletia>
>>>>
>>>> I expect that I am missing something obvious here
>>>> a little nudge may help.
>>>>
>>>> Regards;
>>>>
>>>> Greg
>>>>
>>> What you are missing is that the concept only applies to small integer
>>> (2 or 3) division ratios and won't work as speculated here. It's sort
>>> of (long stretch here) like injection locking in reverse. If you want
>>> I'll try and post some links to papers later.
>>>
>> Nonsense, its already been done for much larger ratios and they need
>> not be integers.
>> Try simulating it.
>>
>> Bruce
>>
> One counter example to the simplistic statement about the operating mode
> of a regenerative divider being restricted to division by small integers
> only, is that such analysis appears to preclude the possibility of using
> a regenerative divider to produce a frequency comb. Unfortunately a
> regenerative divider has already been used to produce a low noise
> frequency comb where the comb frequency spacing is f/n(where f is the
> input frequency and n is an integer). Its possible to extract a
> frequency that is a rational fraction (m/n where m and n are integers)
> of the input frequency from such a regenerative frequency comb. Thus
> there is at least one method of using a regenerative divider to produce
> a 10MHz signal from a 26MHz signal.

As I recall it, in the generalized regenerate divider where two 
frequencies is filtered these match up

http://tf.nist.gov/general/pdf/1800.pdf

The two frequencies f1 and f2 has the sum of the input. This has the 
side-consequence that

f1 = fin - f2
f2 = fin - f1

which is also the conversion steps that the phase will experience over 
two turns around the loop. For synchronous operation the aggregate phase 
becomes 0 degrees (modulus 360 degrees).

Considering that fin = 26 MHz and f1 = 10 MHz we can conclude that f2 
needs to be 16 MHz.

As for avoiding asynchronous operations the above NIST articles gives 
some addtional hints on page 3, among which keeping the loop short is 
among the important onces, essentially that the electrical delay length 
doesn't support many modes. Keeping all traces on a normal PCB for 10 
MHz and 26 MHz should avoid that issue completely.

This would form a 5f/13 - 8f/13 system since 2 MHz is the common 
frequency for all of these. Keeping phase solutions unique for 2 MHz 
separation should not be too hard.

Cheers,
Magnus




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