[time-nuts] PRS-10 Missing SP values in Appendix A.

[Dana Whitlow]

Thanks Forrest,

I've added this to my documentation packed for my own PRS-10; I suspect
that I'm
only a year or two from (possibly) needing it myself.

Dana


On Fri, Sep 13, 2019 at 3:00 AM Forrest Christian (List Account) <
lists at packetflux.com> wrote:

> Mainly wanting to post this to the list so it will end up in the archives.
>
> So I decided to give calibration/adjustment of my bench PRS-10 a go.
>
> What I discovered is that on my particular unit, the frequency was enough
> off that in order to bring it close to spec, I had to adjust the Mag Offset
> to the lower end of it's range (2300), and even then the set frequency was
> lower than I would have liked.
>
> According to the section of the manual under the SP command, if the Mag
> Offset is at the end of it's range, you can change the frequency
> synthesizer's parameters by querying the existing SP? settings, finding the
> row in Appendix A which corresponds to those values, then changing the SP
> value up or down a step (by using the values in the table row just above or
> below the value).
>
> In my unit, the SP value set (6114,3436,29) were not anywhere to be found
> in Appendix A.
>
> After some digging, and reading the manual, I discovered that these values
> are used to configure the  MC145193 inside the PRS-10.   Specifically the
> first value (R) is used to divide the 10Mhz output.   The second two values
> (N, A) are used to divide 359.72Mhz (which is related to the Rb
> frequency).   This second divisor is calculated by (N*64+A).  The resulting
> two divided down signals will be very close in frequency, and the
> difference is used to stabilize the oscillator.
>
> After some more work, I discovered that the divisor values currently in my
> oscillator were actually exactly 3 times the value of row 52, that is
> 6114/3=2038 and (3436*64+29)/3=(2038*64+31).   Since it's only the ratio
> between the divisors which matter, I'm assuming someone at some point
> decided to use the higher division ratio for some reason.  Not sure if this
> was at SRS or in the field.
>
> After discovering this, I followed the procedure to move the SP values by
> one row in the table, and everything seems to have re-centered itself.
>
> Hope this helps someone...  Even if it's me in the future if I have to do
> this again.
>
> --
> - Forrest
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