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

[Bruce Griffiths]

Magnus Danielson 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
>
Attenuating the sum frequencies fin + f2 (36MHz) and fin + f1(42MHz) 
sufficiently (~10dB or so) is also required.
The 10MHz and 16MHz bandpass filters in the feedback loop should easily 
accomplish this.

Its also possible to use a cross coupled pair of mixers where

the first mixer has 26MHz and 10MHz inputs producing a bandpass filtered 
output at 16MHz

the second mixer has 26MHz and 16MHz inputs producing a bandpass 
filtered output at 10MHz.

The 10MHz output from the first mixer drives one of the 2nd mixers 
inputs whilst the 16MHz output from the second mixer dries one of the 
first mixers inputs.

This can simplify the filtering.

Another variant uses a pair of cross coupled lower sideband mixers.

Bruce

Bruce