dave wrote:
[...]

You need UV radiation to energize the upper atmosphere. Sunspots are
where the UV rays come from. It's in your Extra Class test.



Yes, I know about the ionosphere. But what I am trying to say is
that more radiation is not always "better." And there's always some,
even at sunspot minima.

For example, during the bottom of the solar cycle, 75 meters is
alive during the day, with stations heard many hundreds of miles
away with good signals. Near the top of the cycle, the absorption is
so high, you can hardly hear any stations at all daytimes on 75.


With all good wishes,


Kevin, WB4AIO.
--
http://kevinalfredstrom.com/