Broadcasting is the transmission of radio and television programmes via cables, ground-based transmitters, satellites and the internet. There are thousands of different TV channels around the world, broadcasting entertainment, news, information and sport. TV programmes are created at television stations. Some programmes, such as news and sports, are broadcast live, which means the viewers see action as it happens. Most programmes are recorded and broadcast at a later date.

TV studio

Television programmes such as news, discussions and games shows are made in a large room at the TV station called a studio. Each programme has its own backgrounds and furniture called a set. Cameras and microphones send signals to the control room. Lighting comes from powerful lamps. The camera operator steers the camera while checking the picture in the viewfinder. The floor manager also works in the studio. He or she makes sure everything runs smoothly.

Control room

Pictures from the cameras in a television studio, and from cameras at outside broadcasts, such as sporting events, are fed to a control room, where they appear on screens. Responsible for what pictures we see on our screens, the director gives instructions to the people in the studio and the vision and sound controllers. Live pictures from cameras, pictures from videotape (such as short news reports) and computer graphics may be mixed to create the signal for the pictures that will be broadcast. Sound from microphones is added.

Terrestrial, cable
and satellite

In terrestrial TV, the signal goes to a transmitter where it is turned into a signal that is spread out in all directions. TV signals are transmitted using radio waves. Different channels are carried by waves of different frequency (the number of waves sent out each second). The signal can be detected by an aerial within range of the transmitter.

In cable TV, the signal travels from a cable TV station through a network of underground cables made of optical fibres. The signal is then converted to an electrical one and travels to the television receiver via a coaxial cable (a cable that has a conducting wire contained in an insulating layer, itself surrounded by a wire "shield").

In satellite television, the signal is beamed by microwaves to a satellite orbiting the Earth. The satellite detects the signal with its antenna and re-transmits it so that it can be picked up by receivers on the Earth’s surface.

Aerials and dishes

Terrestrial TV signals are broadcast from transmitters (1) at the top of tall masts, often on hill tops, and detected by aerials (2) placed high up on roofs. This gives the signals a clear route from transmitter to aerial. But in mountainous areas the signals are often blocked by hills. This is not a problem with satellite TV, where the signals come down from a satellite high in the sky to small aerial dishes (3) aimed accurately at the satellite.

TV broadcasting satellites sit directly above the Earth’s equator, about 36,000 kilometres (22,000 miles) up, in an orbit called a geostationary orbit. They orbit at the same rate as the Earth turns, which means they always stay above the same point on the Earth’s surface. TV signals are beamed to them by microwaves from dish aerials at a ground station. The satellite transmits a broad signal beam which covers a wide area when it hits the surface. Any receiver in the area can detect the signal.

Webcasts

A webcast uses streaming media technology to distribute a TV programme to many listeners or viewers via the internet—another form of broadcasting. The development of this technology has allowed a number of small, independent TV companies, as well as the big established broadcasting networks, to produce their own shows and broadcast them over the internet. A "wedcast", for example, allows video footage of a wedding in a distant location to be shown live to friends and family over the internet.