Radio Waves, Frequency, Amplitude, and Modulation

Radio Waves

Properties of Radio Waves are electromagnetic waves that travel at the speed of light (approximately 300,000,000 meters per second). Wavelength is the distance between two ‘peaks’ or ‘troughs’ in the wave. It is measured in meters and represented by the Greek letter lambda (λ). The shortest wavelengths are just fractions of the size of an atom, whilst the longest wavelength currently studied by scientists is larger than the diameter of the Earth.

Frequency

The frequency of an electromagnetic wave is defined as the number of waves that pass a fixed point in a given amount of time. It is measured in Hertz (Hz), where 1 Hz is equal to one wave passing a fixed point in one second. Since the speed of light is constant, the frequency of a wave and its wavelength are inextricably linked. The higher the frequency the shorter the wavelength, and vice-versa.

Amplitude

The amplitude of a wave is the ‘vertical’ distance between the peaks and troughs

Modulation is the process by which information is ‘added’ to radio waves in order for it to be conveyed from one location (the transmitter) to another (the receiver). The carrier wave will have a constant periodic waveform – effectively a ‘blank’ wave at a given frequency and amplitude, say for instance 125 MHz. To add information – for instance, a voice signal – to this ‘blank’ waveform, it must be modified by a device called a modulator. The two most common methods of modulation in use are Amplitude Modulation (AM) and Frequency Modulation (FM). Most people will be familiar with these terms because they are used in analogue commercial radio broadcasting. In amplitude modulation, as the name suggests, it is the amplitude of the carrier wave which is varied in relation to the message signal. In frequency modulation, the frequency of the carrier wave is varied in relation to the message signal. The image below shows how the same voice signal (the modulating wave) is combined with the constant carrier wave in both AM and FM modulation methods.