[time-nuts] Re: pulling some crystals

[glenlist]

Hi Jim

a recap : The thread started with the aging issue and having enough pull 
to deal with 10-15 years of aging.

DDS : that is a good point, and I have done frequency references doing 
just that- That is to say ,  to hell with the source frequency, just 
adjust the DDS to give you the frequency that you need.  I did this for 
some ham stuff-

The DDS should be able to meet the requirements- but it would need to be 
clocked alot faster to get the output I want. And of course I have to 
make that higher clock --- (cannot use internal DDS multiplying PLLs - 
they are quite noisy).  which sort of adds an extra layer of complexity. 
and the fast  big DDSs are expensive (comparitivly) .

  .....yeah could lock my 98.304 oscillator  a lower oscillator , but  I 
will do that anyway, my issue is the aging . I also need to reduce the 
number of oscillators on the board because their fundamental (and 
harmonics) will be heard by the ADC that is looking at FSD - 120dB ! so  
one reason to go such a high reference is to reduce birdie opportunities...
But, your suggestion I will take a 2nd think about.

The aging is the unknown killer (and the DDS would sort that - admit) 
although I'd need to look at if the frequency step was available (IE DDS 
resolution)Â  to keep a number of them within 0.1ppm of each other.

the sample clocks produced by the rather good synthesisers (believe it 
or not) are around 392 MHz. (98 x 4).

The ADF4356 is a bl00dy ripper of a device.  It is VERY impressive but, 
$$ and power power. There is also the LMX2572LP I use  which is $ and 
low power, but almost as good at a quarter of the price. and power.

I use both in my designs..

On 13/12/2023 6:02 am, Jim Lux via time-nuts wrote:
> I can't remember where this thread started, but do you actually need to move the oscillator at all? Or is "knowledge" good enough?
> For instance, could you have a (high quality) DDS to generate a desired frequency, and the commanding of the DDS is done by comparing your oscillator and the 1pps from external reference.
>
> This may or may not work, depending on your phase noise requirements.  There are techniques for DDSes to make the close in phase noise small (at the expense of raising it farther out - it's always like squishing a balloon).
>
> Or some other technique of taking a quiet, but movable, oscillator and locking it to your "good" oscillator (and using GPS to set the relative frequencies).
>
>