Hi
> On Apr 14, 2018, at 11:10 AM, Adrian Godwin <artgod...@gmail.com> wrote: > > What if you iterated toward a suitable minimum-error setting, then looked > for cyclic corrections with a period of weeks to months. Once you start to > see that, choose the centre of the cycle and track it (or perhaps just > increase the time constant). If you only get one data point per month, then it will be a pretty basic plot. Even with a data point a week, it will be pretty sparse. We get very used to “data everywhere” sorts of situations. With most of the proposed approaches *if* tight set is desired the data will be pretty sparse. It’s still a bit unclear what the target accuracy is (or even if the TCXO needs setting at all …). Bob > > On Sat, Apr 14, 2018 at 2:37 PM, Bob kb8tq <kb...@n1k.org> wrote: > >> Hi >> >> The gotcha is that you do not have a calibrated adjustment. Put another >> way, >> there isn’t a perfect correlation between DAC bits and ppm. Each >> adjustment >> you make is subject to a bit of error. When you are trying to get within a >> ppm, >> your measurements are quicker, so the larger error ( percentage of step) >> may >> not be as big a deal. When you get close, it is likely to become a big >> deal. >> >> You could track all of your changes (month to month). The issue there is >> that the >> drift in the TCXO month to month is not likely to be the same. Sorting all >> of that out >> could be a bit nasty ….. >> >> ==== >> >> TCXO drift is not the only contributor to the accuracy of a time code >> generator. >> The other obvious one is setting it to the correct time in the first >> place. If the >> objective is to compare data from different locations, getting it set may >> be as >> big an issue as the TCXO. If it’s a single location and the time is >> arbitrary, then >> maybe not so big a deal. If it’s all arbitrary … why worry about drift? …. >> >> GPS on the board looks like a good thing to have to me …. >> >> Bob >> >> >>> On Apr 14, 2018, at 6:35 AM, Adrian Godwin <artgod...@gmail.com> wrote: >>> >>> If you compare VCXO time with UTC or GPS once a month to an accuracy of >> 1s >>> (with NMEA or even a time signal and manual pushbutton) and make a >>> correction for the 2.5 million seconds that occurred since the last >>> correction, you'll be better than 0.5 ppm. >>> >>> Is that good enough ? >>> >>> On Sat, Apr 14, 2018 at 5:59 AM, Hal Murray <hmur...@megapathdsl.net> >> wrote: >>> >>>> >>>> kb...@n1k.org said: >>>>> The alternative is to plug a USB GPS into the mac and do a bit of code >> to >>>>> compare things. If you want to pass the gizmo around to your friends …. >>>> that >>>>> can be done. Pretty good ones are “sub $10” delivered. >>>> >>>> USB GPS gizmos generally don't have a PPS and the timing on the NMEA >>>> sentences is generally crappy. (I may be biased by a few bad examples.) >>>> >>>> Does anybody have a list of ones known to work well? >>>> >>>> There is at least one GPS-USB with PPS, the Navisys >>>> GR-601W/GR-701W/GR-801W, >>>> They were hard to get retail. Looks like idealez sells them Taiwan for >>>> $47 >>>> for the 701W (Ublox 7), $50 for the 801W (Ublox 8) (plus shipping). I >>>> haven't tried ordering through them. Gary and/or Mark may have some for >>>> sale. >>>> >>>> ---------- >>>> >>>> Plan B is a GPS breakout and a USB-serial breakout and a few wires. 4x >>>> less >>>> USB jitter if your USB-Serial chip is full-speed. >>>> >>>> I got mine from SparkFun: >>>> Venus GPS with SMA Connector >>>> https://www.sparkfun.com/products/11058 >>>> USB to Serial Breakout - FT232RL >>>> https://www.sparkfun.com/products/12731 >>>> >>>> ---------- >>>> >>>> Google found this. I don't know anything more: >>>> https://www.zti-communications.com/z050-gps-dongle/ >>>> >>>> >>>> -- >>>> 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. >> > _______________________________________________ > 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.