Hi They are constrained by the same basic TCXO issues that give you sawtooth correction. They do not use EFC to get the TCXO on frequency. With sawtooth they give you a word that lets you know what’s going on. With the NCO’s they often are doing very crude synthesis. They don’t put a $48 DDS chip in a $10 GPS module. If you put one on a spectrum analyzer, it’s not pretty ….
Bob On Aug 19, 2014, at 5:46 PM, Said Jackson <[email protected]> wrote: > Tom, > > Btw part of my frustration with this is that we sometimes get calls from > customers asking why they need our or others' GPSDOs for a couple 100 dollars > when they can buy a CW or uBlox doing "the same thing" for a fraction of the > cost. > > Most of them come back to us after evaluating these NCOs and finding that its > not the same thing. > > You get what you pay for I guess.. > > Said > > Sent From iPhone > >> On Aug 19, 2014, at 13:01, "Tom Van Baak (lab)" <[email protected]> wrote: >> >> Hal, as long as you maintain long-term phase lock it's a disciplined >> oscillator. So, yes, a carrier tracking WWVB receiver with sufficiently >> stable flywheel LO is a WWVBDO. >> >> Said, too-short or too-long 100 ns cycles is one thing. Still ok for many >> applications. But tell me more about extra or missing pulses in the ublox-7. >> That sounds like a show stopper to me. >> >> /tvb (i5s) >> >>> On Aug 19, 2014, at 2:05 PM, Hal Murray <[email protected]> wrote: >>> >>> >>> [email protected] said: >>>> its not a GPSDO though, not even a simple one :) >>>> It does not discipline an oscillator. It generates the output by >>>> mathematically calculating how many phases it has to add/drop in a second, >>>> then digitally adds/drops/extends/retards the phase of the output clock >>>> to >>>> achieve an average of number of desired clock cycles. >>> >>> Is there something about the term GPSDO that says I have to do the "D" in >>> the >>> analog domain rather than the digital domain? >>> >>> I agree that current technology doesn't give results that are useful for >>> many >>> applications that currently use GPSDOs. What if the clock ran at a GHz? >>> 10 >>> GHz? Sure, it would have spurs, but would it be useful for some >>> applications? >>> >>> Is a GPSDO still a GPSDO if the D/A driving the VCXO only has a few bits? >>> How many bits does it need to be a real GPSDO? >>> >>> Is a battery powered wall clock listening to WWVB at 2 AM a WWVDO? It's >>> got >>> a pretty good ADEV if you go out far enough. >>> >>> -- >>> These are my opinions. I hate spam. >>> >>> >>> >>> _______________________________________________ >>> time-nuts mailing list -- [email protected] >>> To unsubscribe, go to >>> https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts >>> and follow the instructions there. >> _______________________________________________ >> time-nuts mailing list -- [email protected] >> To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts >> and follow the instructions there. > _______________________________________________ > time-nuts mailing list -- [email protected] > To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts > and follow the instructions there. _______________________________________________ time-nuts mailing list -- [email protected] To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there.
