Thanks Bob, I have a spare oscillator, so it's a simple deal to put a meter on it, now that I know what to look for.
Bob >________________________________ > From: Bob Camp <li...@rtty.us> >To: Discussion of precise time and frequency measurement <time-nuts@febo.com> >Sent: Thursday, November 7, 2013 6:27 AM >Subject: Re: [time-nuts] Trimble 34310-T EFC Question > > >Hi > >…….unless the oscillator has a bias / attenuator network internally to shift >the region of the varicap’s capacitance/voltage curve the efc affects. That’s >often done to modify the linearity of the tuning curve. > >It’s pretty simple to check. Put an ohm meter on it and see what it reads. >Check on a couple of ranges in case you are forward biasing something. > >Bob > >On Nov 7, 2013, at 6:09 AM, Charles Steinmetz <csteinm...@yandex.com> wrote: > >> Bob wrote: >> >>> I think I may need to change the LPF feeding the EFC in my GPSDO to get rid >>> of dithering jitter. Is there any point in adding a resistor and cap in >>> the EFC line, or do I need to go back and change the values in the op-amp >>> circuit feeding it? Currently an op-amp directly feeds the EFC pin. I >>> guess this boils down to something like: is there any meaningful current >>> flow in EFC circuit in this oscillator? Or should I add them but will I >>> probably have to change the existing filter, as well? >> >> Generally, an EFC pin connects internally to one or more varicap diodes, >> which by definition must be reverse biased (thus, the only current flow is >> the reverse current (leakage) of the diode(s)). There is often an internal >> series resistor of 50-100k between the EFC pin and the diode(s). It is >> common to use an additional, external series resistor and shunt capacitor, >> generally 10-50k and anywhere from 0.01uF to tens or even hundreds of uF, >> depending on the application. Of course, this additional pole needs to be >> taken into account in the loop stability analysis of the PLL. >> >> Best regards, >> >> Charles >> >> >> >> _______________________________________________ >> 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. > > > _______________________________________________ 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.
