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

[Bob kb8tq]

Hi

Ummm ….. errrr ……

The divisors run down to an output port. There has to be a filter at that port to 
knock down the noise and make the loop close properly. When you multiply the
divisors by three, you cut the frequency at that port by three. You also have a 
significant impact on the control loop…..

Probably a good idea to make sure your board has the “normal” components on
it that correspond to the numbers in the manual. There may have been a running 
change at some point that is not reflected in the doc’s.

Bob

> On Sep 13, 2019, at 12:12 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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