Radio Waves and Frequency
What Are Radio Waves?
Radio waves are a type of electromagnetic energy — the same family as light, but at much lower frequencies that our eyes can't see. They travel at the speed of light (300,000 km per second) and can pass through walls, travel over hills, and bounce off the ionosphere to reach the other side of the world.
Frequency
Frequency is how many times per second the radio wave oscillates (goes up and down). It's measured in Hertz (Hz).
- 1 Hz = 1 cycle per second
- 1 kHz (kilohertz) = 1,000 Hz
- 1 MHz (megahertz) = 1,000,000 Hz
- 1 GHz (gigahertz) = 1,000,000,000 Hz
Example: Your local FM radio station broadcasts at about 100 MHz — that's 100 million oscillations per second!
Wavelength
Wavelength is the physical distance of one complete wave cycle. Higher frequency = shorter wavelength.
\( \text{Wavelength (m)} = \frac{300}{\text{Frequency (MHz)}} \)
Examples:
| Band | Frequency | Wavelength |
|---|---|---|
| 80 metres | 3.5 MHz | ~86 m |
| 40 metres | 7 MHz | ~43 m |
| 2 metres (VHF) | 146 MHz | ~2 m |
| 70 cm (UHF) | 435 MHz | ~70 cm |
Why this matters: Amateur radio bands are named by their wavelength — the "2 metre band" is around 146 MHz because the waves are about 2 metres long. Antenna length is directly related to wavelength, so knowing this helps you understand antenna sizes.
The Radio Spectrum
Radio frequencies are divided into ranges:
| Range | Abbreviation | Frequencies | Amateur Use |
|---|---|---|---|
| High Frequency | HF | 3–30 MHz | Long-distance (worldwide) |
| Very High Frequency | VHF | 30–300 MHz | Local/regional, repeaters |
| Ultra High Frequency | UHF | 300–3000 MHz | Local, repeaters, digital |