Satellite Communication

Today it is possible to talk, fax, e-mail. Telex, transmit data both audio and video via satellite. The impact of the technology permeates every aspect of modern life. It has stimulated the global market place for goods and services and the media market place of views and opinions.

Satellite communications are evidenced nowadays, in every news program seen on TV. Without satellite technology these news broadcasts would rely on film camera and processing before the public could see pictures, with the help of it we get instant coverage of sports, politics, conflicts and disasters.

Satellite communication technology has created universal, high quality, cost effective international telecommunication services. The strength of satellite communications lie in the ability for rapid deployment compared with other media and the ease with which distance can be covered. Other media require the ocean floor to be cabled or roads to be dug up over considerable distances. Satellites, once place in the right orbit, can be used for communications from anywhere on earth through a briefcase-sized terminal which takes only minutes to erect. In the same way, from dishes no more than 50-cm diameter homes can receive direct TV broadcast by satellite.

There are, of course, some drawbacks, but they are gradually being overcome. One of the worst drawbacks is the delay introduced by distance traveled to and from the satellite. As these problems are overcome so the satellite is seen as a suitable medium to complement optical fibre cable. In general it is considered that fibre is suitable for thick routs. Satellite is a good medium for thin routs. Satellite is also a good back up for fibre submarine cables.

The most popular orbit at present is the geostationary orbit at a height of 36000 km. A worldwide cover can be achieved with only 3 satellites. There are two types of communication: these are real time and delayed.

Television

Television as well as radio is based upon the use of radio waves. In a television system two separate transmitters are employed – one for the sound channel and the other for the picture channel. Each transmitter has its own antenna. The sound transmitter is frequency modulated and transmits the sound which accompanies the image.

The image being televised is received by the television camera, which converts electrical impulses into optical impulses. These electrical impulses are amplified by the video or picture amplifier. After proper amplification the video signal modulates the high-frequency carrier of the television transmitter and radiated into space by the aerial. The picture carrier is amplitude modulated.

At the television receiver, the picture and audio signals are picked up by a single antenna. Two separate intermediate frequency amplifiers are employed; one for the picture signal, and the other – for the sound signal. The sound intermediate frequency signal is demodulated by the loud speaker in the usual way. The picture intermediate frequency signal is amplified by several stages and then fed into the video or picture detector, where it is demodulated.

The picture reproducing device is a cathode-ray tube. It consists of a glass envelope, a source of electrons or a gun, a control grid for varying the intensity of the electron beam and a screen. The screen is covered with a fluorescent material, which glows when struck by a stream of electrons from the gun. A color television has three electron guns – one for each of the primary colors – red, blue and green. They bombard a screen of phosphor dots, arranged in groups of three – one dot for each color.