2.2 Basic Radio Wave Propagation

Propagation refers to the way radio waves travel from one place to another.

In aviation, radio communication is affected by:

• Frequency

• Wavelength

• Aircraft altitude

• Distance from the station

• Terrain

• Atmospheric conditions

• Transmitter power

• Antenna position and performance

For PPL radio, the two main frequency bands to understand are:

• High Frequency, or HF

• Very High Frequency, or VHF

HF and VHF behave differently because they use different frequencies and wavelengths.

HF has a lower frequency and a longer wavelength.

VHF has a higher frequency and a shorter wavelength.

This difference affects how far each signal may travel, how easily it is blocked by terrain, and how clear the received signal is.

High Frequency — HF

High Frequency, or HF, operates between 3 and 30 MHz.

HF radio waves have relatively long wavelengths, approximately 10 to 100 metres.

HF can provide long-range communication because signals may be reflected back towards the Earth by the ionosphere. These reflected signals are known as sky waves.

This allows HF communication to reach: