[time-nuts] Re: FS740 Thoughts?

[Bob kb8tq]

Hi

The 5 Hz (or whatever) switching and the hump definitely both
originate in the same “feature” of the design. Does disabling the 
switching nuke the hump? If one has a PRS-10 I’d say it’s well
worth trying.

The “filter” in the PRS-10 is not really set up for a GPS sort of 
signal. It’s designed to handle a nice clean lab generated 1 pps.
It’s there to lock the device up as part of a calibration routine. 
The 1 pps sync setups on other Rb’s are designed with the same
target in mind. 

Bob

> On Nov 18, 2021, at 7:50 AM, Dana Whitlow <k8yumdoober at gmail.com> wrote:
> 
> 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.
>> 
> _______________________________________________
> time-nuts mailing list -- time-nuts at lists.febo.com -- To unsubscribe send an email to time-nuts-leave at lists.febo.com
> To unsubscribe, go to and follow the instructions there.