TELECOMMUNICATION

Without moving from the work station ,a nurse can keep track of the several patients in different rooms in the hospital. In their homes, millions of people around the world watch as an astronaut walks on the moon. You dial number on your telephone , and speak to a friend far away. The nurse, the astronaut ,and you are using modern methods of communication. These methods of using electronic equipment to send and receive messages are called telecommunications. The term sages are called from the Greek word tele, meaning "far". The most familiar telecommunication devices in our life today are telephone, radio, and television. The telegraph ,too, was once an important telecommunication device. Since their invention , each of these devices has been improved on a variety of ways. In addition, computers have been combined with these devices- especially the telephone - to provide a great variety of telecommunication instruments.

 

TELEGRAPH-BASED COMMUNICATION

The first telegraph was invented in 1837 by samuel. F.B. Morse, an American short and long electrical impulses over a wire. This was done by pressing the switch key of an electric circuit in a pattern of short and long intervals reached another telegraph instrument some distance away, at the far end of the wire. The impulses caused an electromagnet in the instrument to pull a metal bar, producing a series of clicks in the same pattern as the dots and dashes that had been sent. The system of dots and dashes is called the Morse Code.

Improvements in the telegraph came rapidly. One improvement, multiplex telegraph made it possible to send messages at once over the same wire. Facsimile, a method of sending pictures over telegraph wires, was another improvement. The teletypewriter was a major development. It has replaced Morse Code telegraphy almost completely.

The teletypewriter machine, also called a teleprinter, has a keyboard like that of a typewriter. As the operator types the message, one or more teleprinters in other places receive and type it out automatically. The only limit on the machine's speed is the typing speed of the operator.

Teletypewriters are used by news agencies to send reports to newspapers and broadcasting stations.Telegraph are sent by teletype writers ,and many businesses have teleprinters in their offices. Each machine, like a telephone, has its own number. The operator dials the number of machine to which the messages is to be sent and then types the message. Thus there is a network of teletypeprinters that can "talk" to each other. This network is called TWX or TELEX.

TELEPHONE -BASED COMMUNICATION.

The telephone was invented in 18 76 by Alexander Graham Bell, a Scottish American teacher and scientist. The first telephones were installed the following year. Today there are millions of telephones in the world. In the united states alone the average telephone user makes nearly 1,000 telephone calls a year.

The Radiophone. The telephone became even more useful when radio was added to it. In 1929 the first commercial ship-to shore radiotelephone service was installed on the steamship Leviathan, making it possible for passengers to talk on the telephone at any time during the ocean crossing. Today a telephone user on the move can make and receive calls in a car, train, or boat almost as easily as at home.

In the 1980's a new high-capacity mobile radiotelephone communication system went into service in the major cities of the united states. Known as cellular telephones, these instruments use low-power radio transmitters to cover small geographic cells, or regions. Electronic switching automatically transfers the call from one transmitter to another as the car moves from cell to cell.( before cellular telephones were developed, mobile operators had to connect each call.) With this system, more than 100,000 car radiotelephones can be served in a given city.

The video Telephone.
Video telephone service was introduced in 1969. People using this instrument can also show each other pictures or other objects. A video telephone set consists of a small picture tube, like the screen of a television set, and a camera tube, like those used in television cameras. Each set has a microphone and loudspeaker. There are also switches to turn off the picture. If either speaker wishes to do so. On a larger scale, a communication service called teleconferencing permits a number of people ,each at a different location - even thousands o miles apart- to hold meetings and conferences. They can see and hear one another and can show charts, graphs, and other types of printed material.

Telephone and the computer.
Computer are machines that handle information at very high speeds. Information and instruction taken in by a computer are stored in a part of machine called the memory. When it is "ordered" to do so , the computer performs complex calculations, and prints out information in printed or electronic form.

The rapid growth in the use of computers brought about an important new use for the telephone. It was put to work sending information to computers at a distance. This process is called data transmission. A special kind of telephone, known as the data terminal, was developed for this purpose. Computers are also able to communicate over regular telephone lines. A device called a modern translates computer signals into signals that can travel to telephone wires, thus allowing a computer to "talk" to another computer thousands of miles away.

Modern data systems handle information by digital techniques in both transmission, and connection of calls. They use high-speed, on-off pulses that make up the language of computers. These pulses are called bits(short for "binary digits"), and they are encoded into groups to make up the letters and numbers of ordinary language. Information I digital format can be transmitted at rates of more than 10,000,000 bits per second (bps) . The rate of transmitting information by telegraph corresponds to only about 120 bits per second.

A business that has several branches in different cities may use many small computers and data terminals to connect each branch with a central computer. More and more modern business are transmitting information from one location to another across networks of interconnected computers as well as "peripherals" (electronic and video apparatus connected to the computer).

RADIO COMMUNICATION

The early telegraph and telephone required wires to carry a message. Radio, which is still called the wireless in some places, depends only on waves that travel through space at the speed of light. In 1901 , Guglielmo Marconi, an Italian working in England, used radio to send a dot-and-dash message across the Atlantic Ocean. Broadcasts of voices and music began soon afterward.

Because radio needs no wires, it is tremendous help to ships and planes. All ships now keep in contact by radio in control towers of airfields "talk the pilot in"- that is , people on the ground direct the air -plane pilot so that the craft is landed safely. Police officers in cars and direct them to trouble pots. Many doctors and business people also have two-way car radios.

Amateur Radio.
Amateur radio in an interesting hobby open to people of all ages. Amateur radio operators, also called hams, enjoy talking to other hams over the world. They may use either voice or Morse Code. Amateur often provide useful public service in disasters and emergencies by relaying messages when other means of communication are disrupted. There are now more than 1,000,000 amateur radio operators in the world.

Citizens Band Radio
. Citizens Band Radio, or "CB radio", is another type of amateur radio. It is designed to carry only over short distances. Walkie-talkie radios and similar small, inexpensive transmitters and receivers have made this kind of radio very popular. Especially popular with truck drivers, CB's allow them to communicate with one another over short distances.

Radio Paging.
People who must be reached quickly can keep in touch with the help of radio paging. The person using the pager ,such as a doctor or a service person, carries a small pocket-size receiver like a transistor radio. If the person is wanted on the telephone, a special signal is sent. It causes a buzzer("beeper") to sound in the receiver, indicating that the person should call his or her office or telephone answering service. Radio paging can reach a user who is within about 25 miles (40 kilometers) of the center of a large city, even if the user is inside a building or a car.

.COMMUNICATION VIA TELEVISION

Early experiments in television broadcasting were carried out by AT&T Bell Laboratories in the United States in the 1927. Rapid growth of television began after World War 11. It quickly became one of the world's most popular forms o communication and entertainment. Television reaches millions o people. By a flick of the switch, viewers can enjoy a concert, a lecturer , a play , or a comedy skit. News events can be seen as they happen. Television has become one of the most important mass communication tools.

Cable TV
. Television reception is usually best when the receiver is fairly close to the broadcasting station. A rooftop antenna helps to bring in a clear picture, but the antenna is a little use when the distances are great. In 1950 a method was developed to bring television to isolated communities. The method was Community Antenna Television, abbreviated CATV. It is commonly called cable TV. In a CATV system , a large antenna is set up on a height. An antenna that is high up can "see over" part of the earth's curvature and pick up television signals that will not reach a lower antenna. The signals are amplified(strengthened) if necessary. Then they are fed into a coaxial cable, which carries the signals to individual homes. This special type o wire cable is designed to carry signals a long distance with little loss of strength. Cable TV has expended its scope beyond simply providing improved reception for broadcasting television programs. Most cable companies now originate their own programs. A wide variety of shows and movies are available for a monthly fee "subscription TV" on dozens of separate cable channels. Almost 40,000,000 people now subscribe to cable programs.

Dish Antennas
. The use of dish antennas for picking up television programs as they are relayed by satellites has become possible for private individuals. It is estimated that more than a millions dish antennas are now in use. They are a particularly great value in remote areas beyond the reach of ordinary television broadcast stations or of cable TV.

HOW MESSAGES ARE SENT

When you speak or make a sound , you cause the air around you to vibrate. The vibrations spread as sound waves in all directions. They move like ripples on a pond into which you have dropped a peddle. Sound waves carry, or transmit , the energy reaches someone's ear, he or she hears the sound you made. All telecommunication depends on the transmission of some form of energy has been electrical energy. The transmitter in the mouthpiece of the telephone changes the sound energy of your voice into varying currents of electrical energy. The currents flow through wires to the receiver of the telephone you called. There they cause a thin piece of metal called a diaphragm to vibrate. These vibrations , in turn, cause the air nearby to vibrate, producing sound waves.

One pair of thin wires is all is needed to carry a telephone conversation. Thousands of pairs of these wires can fit into a cable just an inch or two in diameter. Yet many such cables could not carry 40,000,000 long distance calls, and made every working the day in the United States alone. To keep up with the number of calls , and yet avoid the enormous expense of laying down many cables , telephone scientists improved on the multiplex system used in telegraphy. They developed telephone carrier systems, allowing many calls , as voice channels , to be carried on the pair of wires at the same time .

In the 1937 the carrier system provided twelve voice channels on two pairs of wires . Today carrier systems, using coaxial cable, can carry 132,000 voice channels at once . (In coaxial cables, electrical signals do not weaken as much as they do in ordinary cables made of twisted pairs of copper wires.)

Fiber Optics
An important technology, developed in the 1970's and 1980's, has stated to change telecommunications a great deal. This technology, called fiber optics, makes use of pulses of light generated by tiny (size of a pea) laser. The pulses are transmitted over hair-thin fibers of ultrapure glass. The light pulses travel at a rate of 1,200,000,000 bits per second. They are detected at the end of the line and changed into electrical pulses in the form of a digital code. This code represents the voice signal in a telephone communication of the 0-1 (off-on) language of computer, data, and video communication.

The optical fiber can carry much more information than can copper cables or even microwaves , which are described below. One pair of the hair-like fibers can carry pulses of light for 16,000 simultaneous telephone conversations. This means that one optical fiber cable less than half inch (1cm) in diameter can carry more than a million conversations at any time. The first undersea digital light-wave cable system connecting North America and Europe, completed in 1989 , has several times the capacity of an undersea coaxial cable that was put into service as recently as 1983.

The first undersea digital light-wave cable system connecting North America and Europe, completed in 1989 , has several times the capacity of an undersea coaxial cable that was put into service as recently as 1983.

Telecommunication Through space
Much of the work of long -distance telecommunication is done by special radio called microwaves with very short wavelengths- less than 1 foot(0.3 meter) long. Waves that carry A.M radio programs are about l,000 times as long.

Microwaves are well suited for carrying telecommunications. Unlike ordinary radio signals that spread out in all directions from a transmitter, microwaves are sent in narrow , straight beams that can be aimed like a flash-light. Microwaves carrying the signals of long-distance telephone, network radio or television, or other kinds of communications are beamed from tower to second tower about 30 miles (50 km) away. There the signals are received by an antenna ,amplified , and relayed to another tower. A line of towers may stretch for thousands of miles.

Another kind of relay system uses satellites in space instead of towers. The satellite is positioned at a height of 22,300 miles (36,000 km) above earth . It circles the earth at the same rates as that of the earth's rotation, so it seems to hover over one fixed spot on earth. This is called a geosynchronous orbit.

Each satellite carries equipment to detect microwaves sent to it from an earth station. It amplifies the signals and transmits them to other earth stations. The latest satellites can handle 120,000 simultaneous two-way conversations , dozens of color television channels ,or combinations of the two. The antenna of the satellites can receive signals from about one third of the globe. Thus three satellites properly positioned around the earth, can receive signals from any place on the earth, amplify them, and transmit them back to any place on earth.

Switching
The first telecommunication switching systems were human operators for the earth telephone and telegraph networks. Their job was to connect one telephone or telegraph line to another as someone was placing a call. Modern switching systems do the same job but at much faster speeds. While human operators took several seconds to make a connection, the first mechanical switching machines took a few milliseconds (1/1,000 of a second). Electronic machines of the 1970's took microseconds (1/1,000,000 of a second). Today's digital machines operate in nanosecond is so fast that light can travel approximately 1 foot (0.3 meter) in that amount of time.

THE FUTURE OF TELECOMMUNICATIONS

In the coming years, microelectronic devices will be incorporated into all elements of communication systems. Experts predict that by the 1990's , optical fibers will have replaced much of the copper cable that now lies beneath city streets and will stretch across North America , connecting the major cities. Switching and transmitting systems will be almost entirely computerized. Some systems that are already in operation can direct telephone traffic at a rate of over 100 calls per second , or about half a million calls per hour.

There will be more and more communication between people and computers over high speed links capable of handling voice and video transmissions and data of all kinds in the from of digital pulses. Over these systems, computer- based libraries and data banks will expand their capacity for providing reference information, medical data scientific and engineering data, and marketing and financial information in printed or in a picture of in picture format. Experiments on new forms of lasers have shown that information can be transmitted at a rate of 420,000,000 bits per second.

Business and educational conferences will be held by way of video facilities combined with high-quality stereo sound. This will save on transportation and fuel since fewer people will have to travel to meetings. In the distant future, even people who live in different countries and speak different languages will be able to talk to each other. A computerized converter will automatically translate the conversation.

The vast field of communications offers many interesting and rewarding careers. There are jobs for scientists and engineers in developing better communication systems. Office and clerical workers are needed to take care of business operation and procedures. Operators and service representatives are needed to deal with the public. Skilled technicians are needed to install and maintain communication systems. Chemists and physicists are needed to produce the pure crystals and other materials needed for microelectronics.
In the coming years, electronic communication, in combination with computers and microprocessors, will find new uses in business offices and in homes. The "information Age" offers great possibilities for spreading knowledge and improving understanding among the people of our world.

 

Books:Jespersen , James, and Fitz - Randolph , Jane. Mercury's Web:The story of Telecommunications. Atheneum, 1981.
Storrs, Graham. The Telecommunications Revolution. Watts/Bookwright Pr.,1985.
Graham, Ian. Communications. Watts, 1989.

 

  VISIT: for Commmunication magazine Hub and History of communication

3COM Net Age Magazine

Reference
The new book of Knowledge (c) 1994
All rights reserved.

 

Thinkquest Participation 99Edition(http://www.thinkquest.org)
Entry from Royal College Port Louis Students
Mauritius