Popularity of four bands over the years, I compiled it from the spots counts I found on the website. When 20m gets a lot of spots, then 40m is less popular and the other way around. Percentages are on the y-axis.
This is the slightly smoothed solar flux (F10.7) over the same period. I would expect the HF propagation to behave like F10.7, but it should also be noticed that WSPR became more popular over the years.
Last update: 14-Feb-2017