[hpsdr] Horton LO

[Arthur J. Lekstutis]

Hi,

I can't keep up with you guys as I'm too busy with other projects at the 
moment, so I mostly lurk on this list. Perhaps I misunderstand or missed 
an email some place.

Wouldn't a purely digital "fractional N" divider generate significant 
spurs? The duration of any digital signal from a synchronous device 
must, by definition, be multiples of the clock cycle. Trying to get 
around this with a fractional N divider will result in uncertainty of 
the desired output of approximately the clock period. The jitter would 
equal the clock period, the magnitude would depend on the current 
fraction. I would expect spurs from that. Or am I missing something?

Adding a random number generator to a fractional N divider to choice 
when to switch from one frequency to another (which is what I think a 
fractional N divider basically does) might spread out the spurs out, but 
they'll still be there.

I think you need to be happy with an integer divider, or introduce an 
analog PLL, if you want to minimize noise.

Back to lurking....

Later,
Artie Lekstutis
KC2MFS


>***** High Performance Software Defined Radio Discussion List *****
>
>Guido:
>
>Doing all of this fractional stuff digitally and never having to convert 
>back to analog is a big win, a huge win.   The facts are the fractional 
>N, without having to go back to analog, but retaining an all digital 
>character is a huge win since we remove tons of nastiness due to 
>attempting to produce analog waveforms.  Our ULTIMATE resolution should 
>by a 2^16 word size and in this case that is 2.5 kHz.  It is going to be 
>a big win.
>
>Bob
>
>  
>



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