[time-nuts] HP 5065A A1 replacement with DDS

[Hal Murray]

Poul-Henning Kamp said:
> That's one of the reason I went with Bo's DDS (32bit0 instead of the eBay
> modules (20-24 bit).  Higher resolution mitigates the spur problem at least a
> little bit. 

I think it also moves the spurs closer in.  But maybe if they are small enough 
they get lost in the normal noise.

Does anybody have a handy formula for the spurs given the parameters for a DDS?

I've occasionally thought of writing code to generate the output of a DDS and 
run it through a FFT.  I haven't figured out how much memory that would need, 
or rather how wide a DDS I could simulate with the memory I have.  A 20 bit 
accumulator repeats after a million cycles.  At 8 bytes/sample that's 8 
megabytes which I can do.  (Round down if FFT needs another copy.)

We are only interested in the close-in area, so old brute-force calculations 
maybe fast enough.



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