Comm 11-12: HF Radio Propagation

Question 1

Ionosphere

Answer 1

Part of the earth’s upper atmosphere where ions and electrons are present in quantities sufficient to affect the propagation of radio waves
Gives reliable comms over very long distances
Useful for MF and HF frequency bands
Layers
F2 layer
F1 layer
E layer
D layer

Question 2

Factors affecting refraction

Answer 2

Angle of transmission
Frequency
Signal strength
Ion density

Question 3

HF definitions
Propagation path
Skip distance
Skip zone
Fading

Answer 3

Propagation path
The path of radio waves when they are transmitted, or propagated, from one point on the Earth to another, or into various parts of the atmosphere
Skip distance
The distance between the transmitter and the point where the refracted sky wave returns to earth for the first time
Transmission angle, signal strength and ionospheric density remaining the same, the skip distance will be dependent on the frequency
Skip zone
Distance between the end of the usable ground wave and the point where the first sky wave returns to earth
Fading
Fluctuations in the strength of the radio signal at the receiver due to interference

Question 4

MUF

Answer 4

MUF – Maximum Usable Frequency
The highest frequency that will give a skip distance equal to the distance from the transmitter to the intended receiving point

Question 5

OWF

Answer 5

OWF – Optimum working frequency

The frequency which provides the most consistent comms, generally 85% of the MUF