[time-nuts] Programmable clock for BFO use....noise
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.
(I do not use many 12AX7 any more, in real life that is just a down
block in a corner of of a Virtex FPGA. )
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