[time-nuts] Re: FS740 Thoughts?

[Dana Whitlow]

Poul,

You did not really answer the basic question: "Does the 2.5 Hz
(or 5 Hz if applicable) C-field reversal cause the 2-sec bump in
the ADEV plot for  the PRS-10?".

BTW, some radio hams are involved with microwave and even
MMW communications between mobile stations, and I'd bet they
benefit quite a bit from any scheme that reduces magnetic field
sensitivity of their frequency references.  Therefore, the C-field
reversal thing cannot be *all* bad.

Dana    K8YUM


Dana


On Thu, Nov 18, 2021 at 2:41 AM Poul-Henning Kamp <phk at phk.freebsd.dk>
wrote:

> --------
> 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
> phk at FreeBSD.ORG         | TCP/IP since RFC 956
> FreeBSD committer       | BSD since 4.3-tahoe
> Never attribute to malice what can adequately be explained by incompetence.
>