Back to: IREX
Radio Wave Propagation – Frequency and Wavelength
Radio waves are electromagnetic energy transmitted from an antenna, and they travel at the speed of light in all directions.
When you look at a wave shape, the top of the wave is the crest and the bottom is the trough. The distance from one crest to the next crest (or one trough to the next trough) is one wavelength.
If you stand at one fixed point and count how many complete waves pass in one second, that count is the frequency. Frequency is measured in Hertz (Hz):
1 Hz = 1 wave per second
1 kHz = 1,000 waves per second
1 MHz = 1,000,000 waves per second
So when a radio aid transmits in the MHz range, millions of wave cycles are passing every second.
Amplitude is different again. Amplitude describes the wave’s height from the middle (equilibrium) to the crest (or trough). In simple terms, it represents wave strength, not how many waves pass per second.
The key relationship is:
Frequency×Wavelength=300,000,000\text{Frequency} \times \text{Wavelength} = 300,000,000
That constant is the speed of light in metres per second (about 186,000 miles per second).
Because the product stays constant:
Lower frequency = longer wavelength
Higher frequency = shorter wavelength
This is why different radio navigation systems, which use different frequency bands, have different propagation behaviour.
Key Points
Crest = top of wave, trough = bottom of wave.
Wavelength = distance between repeating points (crest-to-crest or trough-to-trough).
Frequency = number of complete waves passing a point each second.
Frequency units: Hz, kHz, MHz.
Amplitude = wave strength (height from equilibrium).
Frequency × Wavelength = 300,000,000 (speed of light, m/s).
Low frequency gives long wavelengths; high frequency gives short wavelengths.