[time-nuts] Re: FS740 Thoughts?

[Poul-Henning Kamp]

--------
Matt Huszagh writes:
> "Poul-Henning Kamp" <phk at phk.freebsd.dk> writes:
>
> > The PRS-10 switches the polarity of the C-field solenoid at 5Hz to
> > cancel out varying external magnetic fields.
> >
> > If that is not a concern for you, for instance because you use it
> > in a stationary application, it can be disabled with the "MS0" command.
> >
> > It's all in the manual.
>
> How does the 5Hz switching relate to the 2s hump in the ADEV plot?

The manual says:

	"[...]the current in the coil is switched at a 5 Hz rate."

You can either read that as:

	"There are five positive and five negative periods every second"

or
	"The sign changes five times per second"

It is not entirely obvious which reading is the correct one.

When I experimented with it ages ago, I concluded the latter fit
my data best, but that was a pretty early firmware version, with
quite a number of variances from the manual.

If your ambient magnetic field is stable, and it should be for
time-nuts purposes, modulating the hyperfine transition is a bad
idea, no matter the frequency.

-- 
Poul-Henning Kamp       | UNIX since Zilog Zeus 3.20
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FreeBSD committer       | BSD since 4.3-tahoe    
Never attribute to malice what can adequately be explained by incompetence.