How does a Video Telephone Work?

            A video telephone is a communication device used foe simultaneous exchange of visual images and the associated speech. In this system one can see the face of the person talking at the other end and also listen to his voice. Do you know how this is possible?

Video Telephone

            A complete video telephone system consists of the following parts:

1.                   Terminal equipment which has a camera display screen microphone and a speaker phone. These instruments transform both voice and visual inputs into electrical signals and vice versa.

2.                  Transmission facilities which carry the electrical signals up to long distances.

3.                  A switching system to allow a choice of terminals to be interconnected. At the transmission point, voice and picture both are converted into electrical signals. Which are carried to a long distance through transmission arrangement? At the receiver end these signals are converted into voice and picture which can be heard and seen by the person at the receiver end.

            Video telephone system was developed in 1927 by H.E. lves who transmitted one way images by wire from Washington D.C. also transmitted from blew jersey to New York by radio. These experiments were aimed at transmitting and reproducing a recognizable human face.

            In 1930, lves demonstrated a two-way video telephone over a wire path in New York City. From 1936 to 1940, a public video telephone service was provided on a local and intercity basis by the German post offices. Call could be set up by appointment between any two subscribers in Berlin, Leipzig, Nuremberg and Munich. A similar system was inaugurated by the soviets in 1961 for subscribers in 8 cities, including Moscow, Kiew and Leningrad.

            Since the 1960s, most major communication agencies throughout the world have been exploring the feasibility of a commercial video telephone service. The first limited commercial video telephone service was offered in the early 1970s by bell system.

            In this system, ordinary telephone wires utilizing specially designed repeaters were used to transmit the video signals. Video requires two pairs of wires, one for each direction of transmission. Early service between Chicago and Pittsburgh provided valuable insight into customer needs, but customer acceptance did not meet the early expectation.

            Nowadays, researchers have developed video telephone systems, using communication satellite links. In many developed countries, this system has now become popular after vase improvement of its mechanism in terms of perfection at the level of customer’s expectation.

What is FM Transmission?

            Over the year frequency modulated FM transmission has attained wide popularity due to its clarity and high fidelity in reproducing the broadcast speech or music. It can also provide a stereophonic effect to the sound produced at the receiving end. Before television came into our homes, radio was a popular entertainment medium. With FM transmission capturing the imagination of people, radio is likely to become popular once again.

FM Transmission Provider

            The earlier transmission services were basically amplitude modulated AM, which could not filter the noise and hence lacked the clarity that FM can provide. But what is the fundamental difference between AM and FM transmission?

            In both AM and FM transmission, radio waves are modulated by mounting it on the carrier frequency, which is essential for broadcasting and propagation. In AM transmission, the waves are constant in frequency but the amplitude varies, whereas in FM transmission, the amplitude is constant and the frequency varies. In simple terms, in AM amplitude is modulated and in FM, the frequency is modulated.

            Modulation is the process of coding the sound waves for transmission, and is done either by altering the amplitude of the wave or its frequency.

            We now need to understand three fundamental concepts- modulating wave, carrier wave and modulated wave. The modulating wave is the information bearing signal such as human voice or music, audible to the human ear, and intended to be communicated to a receiver. The carrier wave can be transmitted over long distances and is not audible to the human ear. The modulated wave is the wave derived by impressing the information bearing signal on the carrier wave. This wave is transmitted through space to the receiver.

            How is it that the FM transmission provides excellent reception?

            Speech itself is represented by an irregular wave pattern. An FM receiver has to detect frequency changes only; it does not reproduce any amplitude changes caused by electrical interferences. As a result, almost all background noise can be eliminated using filters, producing excellent reception.

            FM transmission is used in radio broadcasting services, multi-channel carrier telephones, communication satellite links, telegraphy, mobile communications, navigational and meteorological equipment as well as for medical diagnostic instrumentation. FM also exhibits channel grabbing that is, if two FM signals are available, the stronger of the two is received and the other is nearly excluded. This permits low-power radio stations operating in the same frequency to operate close to each other. AM transmission does not possess this ability.

What is Internet?

            There is hardly anyone who lives in a city and has not heard of internet or used it. It is a fantastic means of communication, education and research. Rapid progress made in the field of information technology has revolutionized the world of communication. The world is gradually shrinking and becoming a global village. Interaction between people of all the countries has become more frequent than ever before. The widespread and effective use of computers in the field of telecommunications has made the world a smaller place to live in.

Internet

            ISD, FAX, Electronic Mail, Paging Service and now internet- all are the gifts of this revolution. Internet has aroused much interest in recent days, as it has become a very powerful medium of communication. But what is internet and how does it operate?

            Internet is the world’s largest computer network. A computer network is basically a bunch of computers connected together by some means, usually telephone links. It is just like a radio or TV networks that can link various radio or TV stations so that they can share a common programmed. The major difference is that in a TV network is that it is one-way communication, and the same information or programmed is sent to all stations.

            In a computer network, a message is usually routed to a particular computer. Some computer networks have a central computer and a group of remote computers that are linked to it- for example, the centralized railways reservation system links many terminal counters to a centralized computer.

            In internet, any computer on the network can communicate with any other computer. Truly speaking, the internet is not really a network; it is a network of networks- all freely exchanging information.

            Through internet, people from all countries can now share information, ideas, stories, data and opinions- the functions that were carried out by letters, telephones and other modes of communication so far. It has become the fastest and most reliable way to exchange information.

            For example, during the 1991 soviet present day Russia coup, a tiny internet network provided all the information to the rest of the world, when all other communication systems were closed. Medical researchers all over the world use the internet to establish and maintain databases of rapidly changing data.

            The internet facilities are provided through a large number of servers. Listing all the services would make the list exhaustive. For example, electronic mail is the most widely used internet service. Electronic discussions and communicate with people over the net. Online chat, information retrieval, bulletin boards, games and gossips challenging other players who can be any where in the world is some other kind of internet services that are available.

            India’s access to the internet has ushered in a new phase of computer communication in the country. Originating as a small electronic community in the American defense department as a way for military researchers to contact each other, internet is now the world’s largest electronic network.