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.
Iunderstand that it can be as bad as a part per million short term
atsome frequencies. The 10 mc and 15 mc broadcasts may be better
orworse at various times of day.
I have spent many hours watching WWVB in the days when they had theold format.
It was good to a part per billion except just beforesunrise and just after
sunset. Then it degraded to either + or -5parts per billion for about 30
minutes.
https://www.youtube.com/watch?v=nf9KWfS9QBs
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