[time-nuts] Re: pulling some crystals

[Bob kb8tq]

Hi

> On Dec 13, 2023, at 4:47 AM, Hal Murray via time-nuts <time-nuts at lists.febo.com> wrote:
> 
> 
> Jim Lux said:
>> 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).
> 
> Could you say more about hat area?  Is there a good paper or chapter of a book?

You modulate the carrier to push the spurs / noise further away from the carrier. To get it working you could be pushing tuning info into the DDS at a “many MHz” sort of rate. That’s going to give you other spurs to worry about. 

> 
> Is there a simple formula for the size and offset of the closest spurs?

There are formulas, to use them you would have to know a lot about the exact defects in the ADC on the example of the chip you have ( = the fine detail of the spurs will vary board to board). The spurs also will vary depending on the tuning setting. This is part of why the “modulation” approach impacts them.

> Do 
> they ever get lost in the phase noise of the main peak?

Not if you look closely. The tricks might get you 10 db … maybe ….

Bob

> 
> 
> -- 
> These are my opinions.  I hate spam.
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