Codan training course material which we use at our head quarters while training people how to use Codan Radio Equipment
- To develop an understaning of how HF radio waves propogate and the effect it has on radio transmission
- Define three types of HF propagation
- Describe the different layers of the Ionosphere
- Describe 3 major Ionespheric conditions which effect propagation
Properties of Radio Waves:
- Waves travel in straight lines
- Waves will be “attenuated” or weakened if they pass through anything that conducts electricity
- The amont of attenuation (and therefore range) depends on frequency and what the wave must pass through
- Increasing power does not increase range in proportion
- Propagation is the word used to describe the way in which radio waves travel from a source to a destination
There are three fundamental modes of propagation:
- Direct Wave
- The radio wave travels from source to destination without interference
- Point to point as in space
- from ground to a relatively close aircraft
Range is short at ground level because the radio wave travels in a straight line and the earth is curved. VHF propagates in a similar manner.
- Ground Wave
- When a direct wave runs parallel to the ground it will follow the ground contours
- It will be absorbed, depending on the moisture in the ground
A ground wave may be considered as bending around the curvature of the earth, but having quite a short range.
- Sky Wave
- When a direct wave passes through the ionosphere it may be weaked by absorption and refracted (bent)
In some circumstances the bending is sharp enough to send the wave back down to earth far away from its source. In this case it is called a “sky wave”.