[GPS_Standard] Controling a Rubidium Standard on the VE2ZAZ Controler.

[Stig Kristiansen - OZ3XO.]

Dear All.

Many thanks for all the surgestions, i will se whar results i get on the 
system, when i have it up and running.

My first wory was for the Controler to exspect a larger change in frequency, 
on the DAC output, as i will realy get, and then i espect the controler go 
go into the Coarse tuning mode, nut again, the Rubidium has to be very close 
to the optimum frequency, so a the fine tuing apears for me, just to be 
better.

I don see a specific Parameter in the Software, to telle the Controler the 
exact tuning range of the user VCXO, to have the correct Loop Gain, but it 
might be possible to adjust the Gain of the R7+R8.

I have chosen the Trimble "Resolution-T" GPS as having a 1PPS jitter of only 
15nS, ( 1 Sigma ), as made specificly for timing purpose, and i vill also pe 
a little paonoide vith stabile DC voltage to all the different components in 
the Circuit, so i gess that only the time will show.

I was acind of exspecting the the comments that ialready received, so i 
therefore first contacted Bert but he surgested that one of you had the 
goldens answer.
Below is the surgeston of the settings that i received from Bert, when i 
asked hem if he in the future will make a Firmware Update, enabling the user 
to telle the Controler, of the Tuning Range of the VCXO, so maby this will 
be a help to others.

By the way, has anyone any results with a Rubidium on the W5OJM Controler 
from QST July 1998, but i gess that it will be almost the same thing ??



Hi Bert.

I am going to use a Rubidium Freq. Std. that only have a tuning range of 
+/-1,5E-9 @ 0-5V-dc, ( 0,03 Hz @ 10 MHz ).
Will that be a problem on yout current PIC Firmware, or will it Requiere a 
new firmware ??

Stig - OZ3XO.



Hello Stig,

I have not personnaly tried the controller board with an oscillator having 
such a small tuning range.
I have reasons though to believe that it would work using long sampling 
periods.
I believe some of the users are running the controller with a Rb oscillator.
My recommendation is that you send an mail on the GPS_Standard mailing list 
at http://mailman.qth.net/mailman/listinfo/gps_standard
Ask if anyone is successfully using it with a Rb unit. you should get an 
answer.

Bert, VE2ZAZ



Hi Bert.

Ok, i might just do that, but i am wondering, if a setting in your Program, 
for entering the Tuning Range of the OSC might be a good idea, so the 
Program know more precisly the right amount of Correction to the OSC, in 
sted af just trying 1 step at the time, og 16 step in the Fast Unlock Mode, 
as the Fast/Slow Mode then might not be needed then.


Stig - OZ3XO



Hi Stig,

The firmware works like this:
If the accumulated frequency offset is larger then the fine/coarse 
threshold, then the firmware will make a step (up/down) of 16 DAC values.
If the accumulated error is less than the threshold, the DAC step will be 
one value.
Everything is a matter of sample period duration. For HP ovenized crystal 
oscillators, we typically use sampling periods of a couple of hours.
The tuning range for those is +/- 0.5Hz. For your oscillator, maybe 12 to 24 
hours will be required to detect a trend and correct the DAC accordingly.
This is the  nature of things:  the smaller the difference, the longer the 
integration period is required to detect that difference.
In any case, experimenting with a few parameters will be required.
This is a good exercise to do!

Bert, VE2ZAZ