They were discovered by Heinrich hertz in 1888, and have the longest wave length in the electromagnetic spectrum.
The wave length of radio waves lies between many kilometres to less than 30 cm (1 GHz). They are mainly delivered by electronic circuits.
But the frequency of electricity at home is 50 cycles per second.
This means that the electromagnetic wave which is radiated has a wave length of 6000 kilometres. radio waves are widely used in daily living.
Thus they are for example used for radios and televisions.
Of course, these use much higher frequencies.
Also almost all electric devices transmit radio waves. Radio waves are transmitted by means of several ranges: Long wave, Medium wave, Short wave, VHF ( Very high Frequency ), UHF( Ultra High Frequency ) and Micro-wave. They are transmitted by a sender and are received by, for example a portable radio. (or your STB).
VHF, UHF and Micro-wave are essentially line of sight.
VHF waves have a small range and reflect against the ground and against large obstacles.
Medium wave Medium skips reflected by the ionosphere and it is possible to get long distance coverage.
Short wave because the radio signals makes innumerable reflected skips between the ionosphere and the surface of the earth, allow a worldwide reception possible.
A Long wave bends itself to the surface of the earth and has, as a result, a range of thousands of kilometres.
Radio waves must reflect from the sender via the ionosphere to the receiver.
These properties are among other things which are dependent on the frequency, the solar activity, the season, the time of the day and so on.
These processes in the ionosphere, important for radio transmission, take place in the air layer to 300 km altitude.
One can consider the ionosphere as a number of isolating air layers separated by more or less conductive layers.
By the presence of those conductive air layers, radio waves on high altitude can be reflected to ground.
As a result, can span large very large distances.
The most important layer with this characteristic is the D-layer, at 70 km altitude, is only by day present.
Most important influence is the weakening of radio waves in the LF and MF range. There no reflection occurs.
E-layer, at 120 km altitude.
This is important for the reflection of radio waves in the KHz range by day, at night these are not present and then can the radio waves reach the following F-layer.
F-layer, at 200 - 400 km altitude.
When at high altitude very large distances can be spanned.
For frequencies above 30 MHz the ionosphere plays no role.
The radio waves reproduce themselves in a straight line.
For a connection between sender and recipient both antennae must line of sight, therefore they must be constructed as high as possible.
In practice the range is less than 100 km in flat landscapes.
Sometimes, there are conditions, as a result of which, larger to very large distances are possible.
For frequencies lower than 4 MHz is by day the weakening of D-layer causes the ground wave to play the major role.
By day reliable distances to 300 km are spanned. At night larger distances can be spanned, but then there is much more atmospheric interference.
Between 4 and 30 MHz the properties of the ionosphere play a major role.
The distance spanned depends on the up beam angle and altitude of the reflection layer.
Because the layers reflect only slanting radio waves, there gaps where no signal is received. there is a minimum skip distance within which no communication is possible.
This distance is between 100 and 500 km and depends on the frequency and the conditions in the ionosphere.
FunFiles Satellite Team