Ed, The tuning pin is the FM pin of the 12.8MHz module. There were several 12.8 MHz references some with 3 pins and then some with 4 pins which used the half rail to set the frequency mid point. It was quite acceptable to program to the closest frequency on the Eprom and pull the reference either by altering the voltage or adjusting to get the offset. It is still then 1ppm stable. Can you tell me which PCB version you have 220-01398-??, I'll she what I have available.
niteviser --- In Repeater-Builder@yahoogroups.com, Ed Yoho <w6yj_ya...@...> wrote: > > niteviser wrote: > > Hi Ed, > > > > The differences I see between the -25 and -26 are minor. Caps and resistors > > in the Low Pass Filter audio stage and a different 12.8Mhz reference with a > > voltage tuning pin, where the standard didn't have it. The specifications > > of the reference are same otherwise, 1ppm -20 to +70. If you are going from > > -25 or -26 to -20, just change the components to the -20 values. Yes, they > > were defined changes for FCC, according to the book. > > > > niteviser > > Aha. Any chance of a PDF with the -26 documentation? What pin on the > DB25 is the tuning pin brought out to? > > I also assume the voltage tuning pin needs to be tied to a stable > reference. The series II schematic shows the "FM" pin (VCXO adjust) tied > to a divider from +5V (not the most stable reference point). > > Thanks, > Ed Yoho > W6YJ >
