The last article described the D layer in the ionosphere. Researchers do know their alphabet. The next layer is "E".

 

It is at 62 to 72 miles out (100 to 115 km). It is lowest portion of the ionosphere that is useful for long distant communications.

 

The E layer, at intermediate atmospheric density, ionization varies with the Sun angle above the horizon, but solar ultra-violet radiation is not the sole ionizing agent. Solar X-ray and meteors entering this portion of the Earth's atmosphere also play a part.

 

Ionizations increases rapidly after sunrise, reaches maximum at noon local time, and drops of quickly after sun down. The minimum is at midnight local time. Similar to the D layer, the E layer absorbs wave energy in the lower frequencies when the Sun angle is high.

 

 

F LAYER. This layer is the area that does the most for long-distance communication. It can be at 100 to over 310 miles out (160 to 500 km).

 

At heights above 100 miles, ions and electrons recombine more slowly, so the observable affect of the Sun develop more slowly. This region holds its ability to reflect back to Earth well into the night.

 

The maximum-useable-frequency (MUF) for the F layer propagation on east-west path peaks just after noon, and the minimum at midnight.

 

The F layer has several factors that affect it as well as propagation. It can get quite involved. Its condition will vary with the time of year, the latitudes, the time of day and particularly what the Sun has been doing from the last few minutes to the last 3 days. The MUF can range from 7 Mhz to 70 Mhz, depending on the described conditions.

 

The F layer during the day may split into two layers. The F1 and F2 layers. The F1 is at about 100 miles up and can act more like the E layer. The F1 layer at night disappears and the F2 layer drops somewhat in height.

 

Much of our RF radiation is refracted by the F2 layer. Depending on the angle our RF enters the F2 layer determines how far this skip will return. The higher the angle, the shorter the skip. If it is too high, it can go straight out and not return.

 

The take off angle is determined by the style and height of your antenna.

 

Every time we operate HF we can see the affects of our incredible ionosphere.

 

73,

Ralph WD0EJA