The ionosphere is the part of the atmosphere where the ions exist and is important to HAM radio enthusiasts because they can use those ions to extend the reach of their radio communications. Knowing the science behind the ionosphere, the frequencies to use and when to use can be an incredible tool for HAM operators.
The atmosphere is divided up into several sections. First you have the troposphere which is the layer closest to earth, then the stratosphere that contains the ozone layer and then you will find the ionosphere. The ionosphere is the most important for shortwave communications and reaches from 50 to 650 km above the earth’s surface.
Most of the atmosphere contains ions that are electrically neutral. The ionosphere gets its name because it is so close to the sun that the radiation actually splits (or ionizes) the ions up into a positive ion and a free floating electron.
There are known to be three layers of the ionosphere. These layers are D, E and F – D being the lowest and F being the highest in the sky. The lower the layer the less dense the ionized atoms are and the most dense is up at the F layer.
The density of air is still pretty high at the D and E layers which means that the ionized atoms quickly come back together. The F layer can remain overnight because the air density is much lower at that time. Radio signals can still be transmitted using the ionosphere at night.
The quality of transmission that you get when using the ionosphere also might depend on what’s happening with the sun. Sometimes the sun has sunspots which are areas of greater ultraviolet radiation. These sunspots increase ionization in the F layer so the higher the radiation, the higher the frequency you would be able to use.
The first layer of the ionosphere is the D layer and mainly attenuates low frequencies. These lower frequencies cause electrons in the D layer to vibrate and when they collide with other molecules, the radio energy is absorbed. Lower frequencies will most likely only ever work at night when the D layer disappears.
The E and F layer are much like the D layer except that the air density is much lower so there are less particles to bounce around and hit each other. This results in less energy absorption and allows the radio waves to remain.
We established that in these layers there are more electrons because these layers are closest to the sun’s radiation. We also established that the air density is less, meaning fewer molecules in the mix. This combination allows the radio wave to be deflected against the dense electrons and bounced back to earth.
Skip distance is a term used to describe how far a radio wave can travel when reflected back from the ionosphere. The skip distance for the E layer is about 2000 km and the skip distance for the F layer is about 4000 km.
Learning about the ionosphere is key for a HAM operator to be able to talk at significant distances and even all the way around the world. Learning to be able to evaluate the sky and the conditions of the sun will help to have greater success with skywave.
The ionosphere is a part of Earth’s atmosphere. There are three layers in the ionsophere that are important for HAMs to know about and those include the D, E and F layers in that order.
The air density is higher at the lower levels which absorbs lower frequencies. At night, the D and E layers disappear making it easier to transmit on a wider variety of frequencies because those layers aren’t there to absorb your waves.
Using the ionosphere is basically a HAM sending a signal up towards the sky at a particular time of day or night and it being bounced back to earth reaching very long distances. The ionosphere is a really neat tool to be able to utilize and having a better understanding will help us to do so.
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