Telecommunication (or telecom for short) is the sending and receiving of information using electricity, radio waves or light. The information can be text, images, sound or video. Telecommunication devices include phones, internet and radio and TV. All these use vast communications networks.

Networks

All the different forms of telecommunication involve signals that can travel through a network. A network may be made up of cables, radio and satellite links. Radio and television networks, where signals are sent out to many receivers from one transmitter, are known as broadcast networks.

​​​​​​​Microwave transmitters and receivers are dish-shaped aerials. A transmitter focuses the microwaves into a narrow beam, which is aimed at a receiver that collects the waves.

Radio waves

Radio waves move through the air at the speed of light. They are used by many networks, including phones, internet and radio and TV.

​​​​​​​To change an electrical signal, such as one representing sounds or video, into a radio signal, the electrical signal is used to shape another signal, called a carrier wave. This shaping is called modulation. It can be done by modulating either the strength of a wave (this is called amplitude modulation or AM) or the frequency of a wave (this is called frequency modulation or FM).

Other kinds of modulation include pulse code modulation (PCM). This is used for sending digital signals. PCM is also used for storing high-quality audio and video signals.

Fibre optics

Fibre-optic communication is another way of sending information, including phone calls, internet and radio or TV signals. Pulses of light are sent through an optical fibre, a fine, bendy thread of glass or plastic about the same thickness of a human hair. The light travels through the core of the fibre by being reflected from one side to another over and over again. The strength of the light pulses is used to encode the signal. This is called intensity modulation.

Mobile phones are radio telephones. They use radio waves for making calls and sending messages. When you speak into your phone, a tiny microphone in the handset turns the sounds of your voice into an electrical signal. A microchip turns this into a digital signal. Each local area, or "cell", has a radio aerial, which receives from (or transmits to) any phone that is inside its cell. The digital signal from your phone is received by this radio aerial and then passed along a network to a phone in another cell.

Internet

The internet is a vast computer network that stretches right around the world. It links together hundreds of millions of computers. Information can travel from any computer on the network to any other computer.

​​​​​​​Internet use falls into two main areas: email and the world wide web. The world wide web (or simply, the “web”) is a huge information-sharing system. It allows computers, including tablets and smartphones, to ask for and copy files from another device. The files are stored in standard form so that any computer can read them. Other uses of the internet include phone calls, video calls and messaging.

Broadcasting is the transmission of radio and TV programmes. There are thousands of channels around the world broadcasting entertainment, news, information and sport.

​​​​​​​The broadcasting station transmits (sends out) radio and TV signals on radio waves (terrestrial or satellite) or by cable in digital form. These are turned back into sounds (and, in the case of TV, moving images) by receivers, or sets. Programmes can also be broadcast via the internet using what is known as streaming technology. They can then be watched on laptops, tablets or smartphones.

TV camera

Television programmes are made using digital electronics. A television camera contains charge-coupled devices (CCDs). The camera "shoots" (captures) the changing scene 25 times a second. As it does so, the CCDs collect light on millions of tiny dots, called pixels. Each pixel measures the brightness and colour (red, blue or green) of that light and the CCD creates a digital TV signal from these measurements.

TV broadcasting satellites orbit the Earth, above the equator, about 36,000 kilometres (22,000 miles) out in space. They orbit at the same rate as the Earth spins, which means they always stay above the same point on the Earth’s surface. TV signals are beamed to them from dish aerials at a ground station. The satellite detects the signals with its own aerial and re-transmits them so that they can be picked up by receivers on the Earth’s surface.