At 12:37 PM 2/7/2007, Mark Amos wrote: >Flexers, > >This is slightly off topic, but I've seen several folks' postings >about tuning to WWV for "pretty good >accuracy". > >I wondered how close one can actually get by tuning to WWV, >practically. I know it depends on where you are, >atmospheric conditions, etc. But what are the practical upper >boundaries to the accuracy of WWV calibration >using the "phase" display, given a stable local oscillator in the Flex. > >I use a GPSDO (at 10MHz) for my "master oscillator". When I tune to >WWV it's always within 1 Hz of where it >was last time I checked. It's typically within .5 Hz or so (based on >how long it takes for the phase display >to cycle) but I haven't done any systematic testing for diurnal >variations, etc.
Propagation probably contributes about 1 Hz (1 sigma) to the instantaneous frequency. Mostly from doppler from moving ionosphere clouds. I have a paper around that tells more detail, and the WWV website at NIST has quite a bit of data on propagation uncertainty. There is a diurnal variation in absolute phase (because the path length changes), and during the transition, the frequency uncertainty will increase. >This is of philosophical / developmental interest to me - I'm >interested in learning more about this. What >are the relative magnitudes of the different factors at play - for >example, does sound card variability >contribute more or less than variability due to propagation, etc.? Depends on the sound card.. My lab measurements on a bunch of Via Mini-ITX form factor boards with built in sound interfaces showed that the variations in frequency from the sound card oscillator were on the order of 1 part per thousand, while the 200 MHz oscillator had variations in the ppm range. >Does the ADC oscillator variability swamp any varibility due to >internal Flex-Radio component drift? questions like that. > >Thoughts on this or pointers on learning more? > >Mark > > > > > > >-------------- next part -------------- >An HTML attachment was scrubbed... >URL: >http://mail.flex-radio.biz/pipermail/flexradio_flex-radio.biz/attachments/20070207/a4ebe217/attachment.html > > >_______________________________________________ >FlexRadio mailing list >FlexRadio@flex-radio.biz >http://mail.flex-radio.biz/mailman/listinfo/flexradio_flex-radio.biz >Archive Link: http://www.mail-archive.com/flexradio%40flex-radio.biz/ >FlexRadio Homepage: http://www.flex-radio.com/ > >FlexRadio Knowledge Base: http://kb.flex-radio.com/ James Lux, P.E. Spacecraft Radio Frequency Subsystems Group Flight Communications Systems Section Jet Propulsion Laboratory, Mail Stop 161-213 4800 Oak Grove Drive Pasadena CA 91109 tel: (818)354-2075 fax: (818)393-6875 _______________________________________________ FlexRadio mailing list FlexRadio@flex-radio.biz http://mail.flex-radio.biz/mailman/listinfo/flexradio_flex-radio.biz Archive Link: http://www.mail-archive.com/flexradio%40flex-radio.biz/ FlexRadio Homepage: http://www.flex-radio.com/ FlexRadio Knowledge Base: http://kb.flex-radio.com/
