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

[Magnus Danielson]

Hi Christian,

Good catch!

If the values is scaled up by a factor of three, the phase comparator
frequency is divided by three. This may or may not be much of an issue,
depending on where on the range one is. Too low comparator frequency is
known to cause an issue thought, but once it is sufficiently high, other
factors tend to dominate on what is the wise choice.

Thanks for reminding me that I need to tinker around with my PRS-10s. :)

Cheers,
Magnus

On 2019-09-13 08:12, Forrest Christian (List Account) 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.
>