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

[Forrest Christian (List Account)]

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