Ionosphere

The ionosphere is defined as the layer of the Earth's atmosphere that is ionized by solar and cosmic radiation. It lies 75-1000 km (46-621 miles) above the Earth. (The Earth's radius is 6370 km, so the thickness of the ionosphere is quite tiny compared with the size of Earth.)

Layers:

Layer	Height	Effect	Active	Daytime Characteristics	Night time Characteristics	Usage
F2	150 - 500km	refract	day and night	Refracts below MUF (~30MHz)	Refracts below MUF (~30MHz)	night-time DX
F1	150 - 500km	refract	daytime	Refracts below MUF (~30MHz)	weak refraction
Es	?	refract	Sporadic	Refracts below 50MHz	Refracts below 50MHz	DX
E	90 - 150km	refract	daytime	Refracts below 10MHz	weak refraction after sunset	working greyline DX
D	60 - 90km	absorb	nighttime	Attenuates <10MHz peak attenuation at noon	minimal	local MF and low HF stations during the day

Bands:

Band	Frequency	Best at	Worst at	Typical use
630m	470kHz	Night	Day	only usable during the night, local
160m	1.8MHz	Night	Day	only usable during the night, local
80m	3.6MHz	Night	daytime	DX at night, local during the day
40m	7.1MHz	Night		DX at night, local during the day
30m	10MHz
20m	14.1MHz	day and night		most reliable DX band
15m	21MHz	day and night
10m	28MHz	day	night	daytime to early evening
6m	50MHz	day	night	daytime to early evening