Hi Having looked at WWV with a Carrier -> BFO -> audio card approach (and a radio locked to an Rb standard …) you have dig a bit to find a situation that is beyond a tenth of a ppm. If you average over minutes or tens of minutes (which is exactly what you do with WWVB) the only time you get past 0.1 ppm is the same sort of day/night propagation mode shift that drives WWVB nuts ….
Bob > On Nov 20, 2018, at 5:35 PM, Donald E. Pauly <[email protected]> wrote: > > That was the first time that I had seen an xy plot of WWV versus a > stable crystal oscillator. It is even worse than I thought. I had to > look up FRK to see that it is a rubidium standard. I talked to Jim > Maxton the chief engineer of WWVB many times around 1995. At the time > I was in Gila Bend 80 miles southwest of Phoenix. He had a Hewlett > Packard cesium standard at Ft Collins. They were using a dual view > GEOS Geostationary satellite to set the cesium to match the master > clock in Boulder. If the cesium was good to 10^-13, that is 8.6 μs > per day. I can't remember how close he tried to keep it or how often > he adjusted it. It looked like that I could determine the start of > the second to the individual transmitter cycle. Time transfer > accuracy was therefore limited to the height changes of the ionosphere > at sunrise and sunset. > > The main disturbance was wind blowing the antenna. Ordinarily the > phase would jitter a few degrees per second. I could tell the wind > speed by the phase jitter without checking the Ft Collins weather. If > memory serves, the loaded Q at 60 kc was about 200. A half percent > tuning error caused a 45° phase error. I have seen a 45° excursions > on several occasions over a minute more than once. My receiver had a > slow lock mode that could spot them. It also had a 45° phase switch > on the 100 kc local oscillator to eliminate the station ID from 10 to > 15 minutes after the hour. There was therefore no disturbance in lock > during it. I was never able to measure any error in the 45° phase > advance. One degree would have been obvious. > > When I first got my receiver going, the phase would advance nearly 40° > at the start of the second when the power was reduced by 10 db. It > had been doing so for years and nobody noticed it. Maxton took an > unneeded condenser out of his time code generator which fixed most of > it. The new transmitter fixed the rest. > > Ft Collins is at 5,003 ft and clocks there run fast by 1.663·10^-13. > (g/c^2)/meter) compared to sea level. How did you correct for > altitude on yours? I presume that frequency is defined at sea level > but I don't know that. Sea level clocks at the North or South Poles > run fast relative to those at equator sea level by 1.192·10^-12. > > WB0KVV > πθ°μΩω±√·÷Γλφ|Δ > > On Tue, Nov 20, 2018 at 9:06 AM jimlux <[email protected]> wrote: >> >> On 11/20/18 1:54 AM, ew via time-nuts wrote: >>> Starting 1970 I used a modified Tracor 599H on WWVB with excellent >>> results. It had a mechanical counter with 100 nsec, resolution. Noisy but >>> perfect. Yes you have to take Ionosphere sunrise and sunset in to >>> consideration and the hourly shift, but being a very early riser 4AM >>> because of Europe no problem. Better than 2 E-11 per day and 4 E-14 per >>> month. >>> >>> In the 90 ties with my FRK having temperature and aging control frequency >>> was better than 1 E-12 all the time. >>> >>> Bert Kehren >>> In a message dated 11/19/2018 9:58:39 PM Eastern Standard Time, >>> [email protected] writes: >>> >>> HF propagation of WWV or WWVH is horrible compared to VLF propagationof >>> WWVB at 60 kc. In this video the 5 mc WWV signal from Ft Collins,Colorado >>> is being received in New Jersey. It was compared against astable 5mc >>> crystal source. You can see a shift of a few cycles persecond over a few >>> seconds. This is due to the movement up or down ofthe ionosphere at a >>> substantial fraction of the speed of sound. >> >> In general terms, the coherence time of the ionosphere is single digit >> seconds - that is, there's essentially no correlation between >> propagation path at one time and the propagation path 10 seconds later. >> >> The "general length" of the path will be the same, but the details >> different. >> >> The actual ionization in the ionosphere can best be described as moving >> "clouds" there's a fair amount of spatial inhomogeneity. In the same >> sense that milk reflects light from a multitude of little fat globules. > > _______________________________________________ > time-nuts mailing list -- [email protected] > To unsubscribe, go to > http://lists.febo.com/mailman/listinfo/time-nuts_lists.febo.com > and follow the instructions there. _______________________________________________ time-nuts mailing list -- [email protected] To unsubscribe, go to http://lists.febo.com/mailman/listinfo/time-nuts_lists.febo.com and follow the instructions there.
