1. AMATEUR RADIO TRAINING Propagation v1.101 © essexham.co.uk

2. PROPAGATION Radio Waves VHF / UHF HF The Ionosphere

3. Radio Waves Travel in straight lines Can be reflected or diffracted (‘bent’) Get weaker as you get further from transmitter Distance depends on a number of factors: Antenna Wavelength Power Obstructions

4. VHF / UHF Range of VHF and UHF is less than that of HF Typically limited to “just beyond line-of-sight” VHF and UHF can be blocked by obstructions, hence antennas are normally located outdoors at high points Antenna position often more important than power

5. The Ionosphere Layer of conductive gases between 70 and 400km above the Earth VHF and UHF signals pass through this layer It diffracts (bends) HF radio waves. Single hop HF signals can be heard well beyond the horizon

6. Ionosphere and HF HF bands are “open” or “closed” at different times of the day Contact around the world is done using multiple “hops” Multiple hop Solar activity has a big effect on the Ionosphere

7. Summary VHF / UHF is generally “line-of-sight” HF signals travel around the world – diffracted by the Ionosphere Ionosphere is a layer of conductive gases between 70 and 400km above the Earth

8. PROPAGATION Any questions? essexham.co.uk/train