62 WIRELESS TRANSMISSION Can you name any household appliances working with this type of wave? Electromagnetic waves Wireless transmission travels through electromagnetic waves generated by the oscillation of an electromagnetic charge. Crest Displacement Wavelength Wavelength Amplitude Amplitude Trough Higher wavelength (lower frequency) Lower wavelength (higher frequency) The name of the frequency unit comes from Heinrich Hertz, a German physicist who demonstrated the existence of the electromagnetic waves predicted by James Clerk Maxwell. Do you know why Bluetooth is so called? If not, look it up on the web. ONLINE RESOURCES Radio waves crest: cresta to join: unire, collegare trough: avvallamento, gola wavelength: lunghezza d onda Electromagnetic waves are characterised by: the amplitude, a, which is the size of a wave from its highest to its lowest point. The greater the amplitude, the higher the energy it carries; the wavelength, , which is the distance from any point on one wave to the same point on the next wave, measured in metres; the frequency, f, which is the number of waves passing a point in a certain time. The unit of frequency is Hertz , which measures one cycle per second. The highest point of a wave is called the crest, the lowest point is called the trough. Electromagnetic spectrum The range in which waves are arranged according to their frequency and wavelength is called electromagnetic spectrum. All types of radio waves are used for radio and TV communications, but: microwaves are usually used in telephone communication, including mobile phones, and also in satellite communication; infrared waves are used in remote controls; 144 ELECTRONICS AND ELECTROTECHNOLOGY visible light is employed in fibre optic communication, as well as in the transmission of images on TV. Applications Mobile (or cellular) networks are wireless communication networks. The network is distributed over areas called cells, in which several base stations are built. These base stations give the cell the network coverage for the transmission of voice, data, and messages. A cell typically uses a different set of frequencies from the cells nearby to avoid interference. When joined together, these cells provide coverage over a wide geographic area. This enables numerous portable appliances, such as mobile phones, tablets, and laptops, to communicate with each other and with fixed transceivers and telephones anywhere in the network, even though some of the transceivers are moving from one cell to another during transmission. Bluetooth technology uses low frequency radio waves. Two or more devices connected through this frequency can exchange files, music, images, or videos at a distance of a maximum of 50 metres.