Hi Tom, last time I looked at these I tried figuring out what they were doing. It is very hard to get measurement data, our TSC did not converge on their signal, and looking at the output on a scope revealed only a bunch of crazy random phase jumps. I guess one could use a counter to measure how many time pulses are being sent in x seconds with x being a large number, or divide the output by 10 million and see how the pulse moves back and forth compared to the 1PPS UTC output.. Since I don't know the exact algorithm being used, I said "adds/drops/extends/retards" in my previous email. I did not mean to imply that the unit is doing all or any of those items. But that is exactly part of the problem isn't it, there is no clear description of what exactly is happening in the uBlox documents or the CW docs for that matter that I could find. I for one would not use that output to drive a processor or other digital device directly, who knows what happens if the processor sees a 100ns, then a 110ns, and then an 70ns pulse if it is only rated at 10MHz and 100ns pulse-width +/- a couple percent for example.. Without knowing the exact minimum phase time period specification that could come out of one of these NCO's, one should not properly use that signal in a digital design. My initial concern was that this is time-nuts, and we should call a GPSDO a GPSDO, and an NCO an NCO in my opinion. Nothing wrong with one or the other, but they sure are not the same thing - by 6 or more orders of magnitude in phase stability. We usually are concerned here about parts per trillion stability and accuracy, and now we are mixing things up that are millions of times worse than one another.. bye, Said In a message dated 8/19/2014 13:08:52 Pacific Daylight Time, t...@leapsecond.com writes:
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 <hmur...@megapathdsl.net> wrote: > > > saidj...@aol.com 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 -- 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.