How Signals Travel

Line of Sight — VHF and UHF

At VHF and UHF frequencies (2 metres, 70 cm), radio signals travel in mostly straight lines — similar to light. This means:

Range is limited by the horizon — typically 20-80 km depending on antenna height
Higher antennas = further range (the signal can "see" further over the curve of the earth)
Hills and buildings can block the signal

Repeaters — Extending Your Range

A repeater is an automated station placed on a high point (hilltop, tall building, tower) that receives your signal and retransmits it at higher power and from a better location. This dramatically extends your range.

You transmit on the repeater's input frequency
The repeater retransmits on its output frequency
The difference between input and output is called the offset (typically ±600 kHz on 2m)

For Foundation operators: Repeaters are your best friend! With just 10 watts and a simple antenna, you can use repeaters to talk to stations 100+ km away. Most 2m and 70cm activity in Australia happens through repeaters.

HF Propagation — The Ionosphere

At HF frequencies (the bands below 30 MHz, like 40m and 80m), something amazing happens — the signals bounce off a layer of the upper atmosphere called the ionosphere and come back down to Earth hundreds or thousands of kilometres away.

This is how amateur operators talk around the world with relatively simple equipment. The ionosphere's ability to reflect signals changes with:

Time of day: Different bands work better at different times
Season: Conditions change throughout the year
Solar activity: More sunspots = better HF propagation on higher bands

Ground Wave

At lower frequencies, signals can follow the curve of the Earth's surface for short to medium distances. This is how AM broadcast stations cover their local area.