Hi Simple answer - good resolution is a challenge to get. It's much easier to modify the Rb to make it pull able.
Bob On May 27, 2012, at 6:08 PM, Michael Tharp wrote: > Greetings, > > I've been pondering topologies for a custom GPSDO design and two obvious > choices seem to present themselves. The first, and seemingly more popular by > far, is to use a "pullable" oscillator as many OCXO and Rb oscillators are > and discipline it using a slow but precise DAC. But unfortunately my Rb is > not pullable so I would have to get another oscillator. So I have a very > stable but off-spec local oscillator, which has to somehow be combined with > the pulse-per-second from the GPS. If there's a palatable analog way to do > this, I'd love to hear, because it would probably be simpler than the other > idea. > > The second obvious idea is to use the local oscillator to clock a frequency > synthesizer (DDS). These can apparently tune a frequency very finely and > depending on how much one spends will produce a pretty clean sine wave even > at 10MHz. Since these also tend to require a FPGA it also fits nicely with > the nanosecond-level phase comparator I've been toying with, and the whole > mess (microcontroller, DDS, phase comp) can all be clocked from some multiple > of the LO without worrying about unwanted phase correlation. Having the GPSDO > be a black box that can transform any undisciplined 10MHz reference into a > disciplined one is very appealing. > > Does anyone have any comments or experience with DDS-based frequency > references? Are they too jittery for this type of application? It will > certainly require quite a lot of creative filtering -- one page I read > mentioned the pitfalls of tempco of phase shift -- but that's just a good > excuse to brush up on my analog design. > > -- m. tharp > > _______________________________________________ > 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.
