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

jimlux jimlux at earthlink.net
Mon Jun 25 10:22:08 EDT 2018


On 6/25/18 6:05 AM, Dana Whitlow wrote:
> A useful hardware demonstration of DDS phase truncation is to do step a DDS
> through a long
> series of frequencies at a relatively low stepping rate, and view the
> output with an FFT-based
> (real-time) spectrum analyzer set for spectrogram display.   Watch this for
> a while and it becomes
> quite easy to reach a practical understanding of what's going on and how
> the spurs behave.
> Note that to avoid confusion from aliasing products, it is a good idea to
> constrain the range of
> frequencies swept to the first Nyquist zone (zero to < 1/2 the DDS clock
> frequency).
> 
> There's a fairly simple regularity in the spur behavior which is not
> particularly obvious from
> looking at equations and tables (at least, not at my math skill level), but
> which jumps out at
> you in the spectrogram display (or even without the spectrogram).
> 



Here you go, as an example:

http://jim-lux.blogspot.com/2018/06/dds-spurs.html

16 bit DDS, 5 bit phase, 4096 samples for FFT spectra, etc.





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