[time-nuts] OT: xtal osc PN

francesco messineo francesco.messineo at gmail.com
Sun Sep 19 19:00:26 UTC 2010


Hi Mike,

On 9/19/10, Mike Feher <mfeher at eozinc.com> wrote:
> Well, if one just looks at the spec of the 10811A for relative performance,
> it is -140 dBc/Hz at 100 Hz offset at 10 MHz. Realistically, probably a
> little better. From that it would be real easy to generate the frequencies
> Frank is looking for, obviously 20 would be easy but would be only -134
> dBc/Hz at 100 Hz away. 22 would be easy by diving the 10 and mixing it with
> the 20, assuming the divide by 5 has a very small contribution, the PN of
> the resultant at 2 MHz is also theoretically 20logN better, so, mixing will
> also give close to -134 dBc at 100 Hz away. 42 can easily be generated by
> doubling the 20, to get -128 dBc at 100 Hz and then mixing with the same 2
> MHz to get the 42 MHz, still resulting in almost -128 dBc/Hz at 42 MHz.
> Obviously filters will have to be used to get rid of the unwanted lower
> mixing products. Depending on the architecture used, as stated below,
> further multiplications will again decrease these numbers by 20logN.
> Filtering at the IF with a 250 to 500 Hz filter is not going to do anything
> to the 100 Hz numbers. I assume the mode of communications here is CW, hence
> the narrow filter at IF. 73 - Mike

this exact approach (well maybe mixing 20 and 22 to obtain 42 MHz
instead of doubling 20 MHz then mixing) was my first choice but I'm
afraid I wouldn't be able to do all these steps without making any
mistake like chosing the right mixer, right filters and
multiplier/dividers.
It was really what I wanted to do, but looks like I could spend too
much time doing it and ending with a poorer result than carefully
chosen xtal oscillators.

Thanks for suggesting it though :-)

Frank IZ8DWF



More information about the time-nuts mailing list