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

[Chris Albertson]

My question about these regenerative filters is that while I know F1 +
F2 = Fin I'm still wondering how stable it is and how you know your
divider will not do something like
10.0001 + 15.9999 = 26.000  for a few hours and then drift over to
9.9999 + 16.0001 = 26.000.    In other words I can see how the filter
keeps the sum locked to the 26.000 reference but I don't see how it
keeps the 10Mhz component stable.



On Sun, Apr 17, 2011 at 3:16 AM, Magnus Danielson
<magnus at rubidium.dyndns.org> wrote:
> 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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-- 
=====
Chris Albertson
Redondo Beach, California