[time-nuts] Re: The amazing $5 timestamper, part 2: discovering a bug in my signal generator

[Poul-Henning Kamp]

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Pluess, Tobias writes:

> In my very first GPSDO I built, I used a STM32F303. This one had a quite
> bad PLL stability, the frequency was varying over time in a sawtooth like
> manner for some reason.

It's called "spread-spectrum" and is done deliberately to game the EMI
criteria for various certifications.

By sweeping the frequency through a range, the peak energy of any one
frequency, as averaged over a second, drops correspondingly.

In many cases you can actually disable it, but you may have to punk the
manufacturer quite hard to find out what bit to set or clear.

-- 
Poul-Henning Kamp       | UNIX since Zilog Zeus 3.20
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