[time-nuts] Programmable clock for BFO use....noise

Gerhard Hoffmann dk4xp at arcor.de
Sun Sep 16 17:56:08 EDT 2018


Am 16.09.2018 um 20:00 schrub Mark Goldberg:
> For a radio BFO you want something with low phase noise (low jitter). The
> SI5351 is not designed for that, and it's jitter spec is 70 ps, which is
> pretty noisy. It even has a spread spectrum mode that would be even worse.
> They do have other parts designed for low jitter (< 1ps). Leo Bodnar's
> GPSDOs with variable output clock frequencies are based on  those chips and
> they provide low phase noise, certainly enough for a radio

Oh, a half of a 12AX7 has always been good enough for my needs as a BFO,
xtal controlled or LC free running. 30 dB above the noise is S5, what more
do you want? The real problems of a receiver are IP3 and that you have
a preselector and a mixer that simply work without producing mess.
LO jitter is probably > 100 times more important than the BFO, that is just
for conversion of IF to audio.

cheers,
Gerhard, DK4XP

(I do not use many 12AX7 any more, in real life that is just a down 
converter
block in a corner of of a Virtex FPGA. )




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