FWIW, I set the DAC to midpoint and use a binary search to get to frequency. On my system, I start off with a change of 0x80 and work my way down to 0x04 in powers of 2 (0x80, 0x40, 0x20, etc). Once I get to 256 seconds between DAC changes, I light the PLL fuse. I could probably get away with less than 256 seconds. Before I built the TIC, I worked down to 0x01 which resulted in pretty long times between changes.
Bob >________________________________ > From: Chris Albertson <albertson.ch...@gmail.com> >To: Discussion of precise time and frequency measurement <time-nuts@febo.com> >Sent: Thursday, April 10, 2014 6:05 PM >Subject: Re: [time-nuts] First success with very simple, very low cost GPSDO > > >On Thu, Apr 10, 2014 at 10:55 AM, Charles Steinmetz ><csteinm...@yandex.com>wrote: > >> >> Why even try to discipline an OCXO before it's warm? Just leave the >> control loop off for a predetermined time at startup. You can light up a >> bright red "unlocked" LED, and even inhibit the 10 MHz output until lock is >> achieved if you want. >> > >Even if you wait long enough you still need to set the DAC to "something" >as a first try. What if your first guess is off by a large amount. The >answer is not to guess better because you still need some way to determine >if the guess is correct. > >> >> Alternatively, you could figure out the EFC voltage needed to zero the >> cold oscillator > > >How to do that? Can you write code to do this without counting overflows? >You can be off by 256 cycles and never know it. Let's assume someone is >building a GPSDO because they need a frequency reference and don't have >one. A good assumption, I think. How could such a person "figure out the >EFC voltage needed" with out either coining cycles? > > >I'm thinking about turning the overflow counter off after lock. But >without one I think we have a chicken and egg problem where you would need >an accurate frequency reference to build a GPSDO. > >-- > >Chris Albertson >Redondo Beach, California > >_______________________________________________ >time-nuts mailing list -- time-nuts@febo.com >To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts >and follow the instructions there. > > > _______________________________________________ time-nuts mailing list -- time-nuts@febo.com To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there.
