[time-nuts] Aging 5065A ?

[Bob kb8tq]

Hi

You could also say that with a longer accumulator, you get a closer approximation to a
desired waveform. 

If you compare the data sheets, the spur levels on the 48 bit parts

ad9854.html <https://www.analog.com/en/products/ad9854.html>
ad9912.html <https://www.analog.com/en/products/ad9912.html>
https://www.analog.com/en/products/ad9956.html <https://www.analog.com/en/products/ad9956.html>

are more related to the age of the part than the width when compared to the smaller parts

https://www.analog.com/en/products/ad5930.html <https://www.analog.com/en/products/ad5930.html>
https://www.analog.com/en/products/ad9834.html <https://www.analog.com/en/products/ad9834.html>

Indeed, if you go through the entire page if parts

https://www.analog.com/en/parametricsearch/11018#/ <https://www.analog.com/en/parametricsearch/11018#/>

There does not appear to be a spur penalty for wider parts. Newer is indeed better, pretty
much across the board. 


Bob

> On Oct 7, 2020, at 8:58 PM, Mike Feher <mfeher at eozinc.com> wrote:
> 
> It seems to me that now since the register so much longer, yet the D/A is the same, updates to the D/A will take longer and therefore creating more close in spurs. That 20logN does suck, but is real. I may suggest running the output of the DDS through a 5 MHz crystal, or better yet a very narrow crystal filter. 73 - Mike 
> 
> Mike B. Feher, N4FS
> 89 Arnold Blvd.
> Howell NJ 07731
> 848-245-9115
> 
> -----Original Message-----
> From: time-nuts <time-nuts-bounces at lists.febo.com> On Behalf Of Bob kb8tq
> Sent: Wednesday, October 7, 2020 7:34 PM
> To: Discussion of precise time and frequency measurement <time-nuts at lists.febo.com>
> Cc: hmurray at megapathdsl.net
> Subject: Re: [time-nuts] Aging 5065A ?
> 
> Hi
> 
> Well….. the existing synth in the 5065 is no champion spur wise. Coming up with a DDS that is “as good as” is not all that crazy.
> 
> The 5 MHz reference is multiplied to 6.x GHz and then mixed with the synth. The close in phase noise of the multiplied signal is mixed with the synth. The output is the sum of the two.
> Going from 5 MHz to 6.x GHz gets you 20 log (N)  … a bit over 60 db added phase noise.
> 
> The synth (at 100 ti 300 Hz offset) needs to be 60 db worse than the noise on the 5 MHz before it even gets in the game. That’s not a really tough spec to meet.
> 
> Bob
> w the instructions there.
> 
> 
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