My Science School

            The 21st century would take people to a world of mechanical solidarity with courtesy from services like paging service, cellular telephone and Internet etc. Having acquainted ourselves with services like cellular telephone and Internet earlier, now let us discuss what paging service is all about.

            Paging is a one-way wireless communication providing instant access to the person being paged. One-way communication means that the subscriber only receives the message and can not communicate back instantly. The subscribers receive messages from anyone with access to a telephone. The modus operandi is as follow: The paging network of a particular region is co-ordinated by a ‘pagers exchange’ or network operator. Subscribers have a paging number assigned exclusively to them by the concerned network operator. The person who wants to send a message to a subscriber rings up the operator and leaves the message with him along with the subscriber’s paging number. Then the operator relays the message to the subscriber either directly or through any other regional operator. The message is then received by a small palm-size device called ‘pager’ kept by the subscriber with himself. An alarm sound from the device alerts the subscriber who then reads the message, flashed on the screen of the device. Some pagers also vibrate to alert the subscriber of an incoming message. The main advantage which a pager provides is that the subscriber receives the message wherever he may be since he carries the wireless device (pager) always with him.

            In India, as of now, the government has issued licenses to private operators to provide paging service to interested people and the number of subscribers is growing fast. As per current estimates, the running cost of a pager for monthly service would be around a couple of hundred rupees and a pager, at the moment, costs about a few thousand rupees. It is now the cheapest and most reliable one-way communication system available in the market today. Although its primary use is to get a message across fast, it has other potential uses such as getting across share market information by the business circles or to have latest cricket scores, for instance. The only demerit is that it provides only one-way communication as the receiver can not communicate back to the caller. 

          Electronic mail is a modern method of instant delivery of letters without the involvement of a postman. In this system of mailing, messages are sent with the help of a computer.

          In the electronic mail system a letter or any other document is typed and edited on a computer. It is then sent to the addressee through a computer network in the form of electrical signals. The addressee may be anywhere in the world but he should also have an electronic mail system. The contents of the transmitted letters or documents get displayed on the screen of the computer of the addressee. If he desires, he can get the message printed. If the addressee is absent, the transmitted matters will be automatically stored in the computer’s memory. When he returns the computer will give an indication that some mail is waiting for him.

          With the help of electronic mail system both typed and handwritten matters can be transmitted. Electronic mail is very fast and saves time and paper work but at present it is very costly. It needs a satellite, telephone and cable links with television, voice and computer data telecommunications. The electronic mail system has so far not been feasible for individual households. This system is being used by developed countries on a large scale.

          Email is widely used in Internet Services. It is also connected to other systems in which exchange of Email are being made effectively.

 

 

          The rapid progress made in the field of Information Technology has revolutionized the world of communications. The world is gradually becoming a global village as interaction among people all over the world has become more frequent than ever before. The widespread and efficient use of computers in the field of telecommunications has made the world a smaller place to live in. 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 in some way or other. It is just like a radio or TV network that links various radio or TV stations so that they can share a common programme. The major difference is that in TV networks the same information programme is sent to all stations whereas in computer network, each particular message is usually routed to a particular computer. Some computer networks consist of a central computer and a bunch of remote stations that report to it - for example, the centralized railway reservation system which links many terminal counters to a centralized computer. But other networks like the Internet permit any computer on the network to communicate with any other. Actually, the Internet is not really a network; it’s 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 are now generally carried out by letters, telephones and other modes of communications. It has become the fastest and most reliable way to move or exchange information. For example, during the 1991 Soviet coup, a tiny Internet network provided all the information to the rest of the world when all other communication systems were shut off. Medical researchers all over the world use the Internet to maintain data bases of rapidly changing data.

          The Internet facilities are provided through a large set of different services. Though to mention all the services would make the list exhaustive, some examples can be given. Electronic mail is the most widely used Internet service. Electronic mailing lists enable one to join in group discussions and meet people over the Net. Online conversation, Information retrieval, Bulletin boards and Games and gossip (challenging other players who can be anywhere in the world) are some other kind of Internet services.

          India’s access to the Internet has ushered in a new phase of computer communications in the country. Originally a small electronic community in the American Defence Department as a way for military researchers to contact with each other, Internet is now the world’s largest electronic network.

 

          Over the years Frequency Modulated (FM) transmission has attained wide popularity due to its clarity and accuracy in reproducing the broadcast speech or music. It can also provide a stereophonic effect to the sound produced at the receiving end. FM transmission service has rekindled the hope of regaining the fading popularity of radio. The earlier transmission services were basically Amplitude Modulated (AM) which could not filter the noise and hence lacked the clarity of FM. But what is the fundamental difference between AM and FM transmission?

          In both cases radio waves are altered for the transmission of broadcasting signals. In AM transmission the waves are constant in frequency but the amplitude of the transmitting wave varies in accordance with the signal being broadcast whereas in FM the amplitude is constant and the frequency varies in accordance with the signal being transmitted. In simple terms, in AM the amplitude is modulated and in FM, the frequency is modulated.

          Modulation is the process of coding the radio wave and is done either by altering the amplitude of the wave or its frequency. Here comes the need of understanding three fundamental concepts: modulating wave, carrier and modulated wave. The modulating wave is the information-bearing signal such as human voice or music. It is the message intended to be communicated to a receiver. The carrier is the wave that is varied by the information bearing signal. The modulated wave is the wave developed by impressing the information-bearing signal on the carrier. This wave is transmitted to the receiver. Now the curiosity arises as to why does the FM transmission provided an excellent reception?

          Speech itself is represented by an irregular wave pattern. As the receiver using FM had to detect frequency changes only, it did not reproduce any amplitude changes caused by electrical interference. As a result, almost all background noise can be eliminated using filters, giving excellent reception.

          FM transmission is used in radio broadcasting services, multichannel carrier telephone, communication satellite links, telegraphy, mobile communications, navigational and meteorological aids 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 be located close to each other. This advantage is not possessed by the AM stations.

 

          Computers have become an integral part of our lives today. Their invasion into every sphere of our life has made them indispensable for us. And the field of media is no exception. Multimedia is the outcome of a sophisticated blending of both visual and audio communications. This explanation is just the tip of the iceberg, the fact remains that it is the integration of various communication networks into our desk that produces amazing results.

          But what is multimedia as we understand it today? Multimedia software combines two or more media for presentation or analysis. It is the result of a co-ordinated work of video, audio and graphics. The earlier personal computers were monomedia as they displayed only one medium. The monomedia computers could not play sounds when they displayed the text on screen. A platform for multimedia emerged with the gradual development of newer technologies that extended the power and scope of personal computers.

          Now one fundamental question arises: what specific functions does a multimedia computer perform? A multimedia computer can recreate the sounds of musical instruments and also it can playback recorded sounds. It can show pictures and movies on the monitor. It can also access information stored on a computer disc. Recorded sounds, movies, pictures and texts have been around for years but what a multimedia computer does is to intertwine these things and produce a combined effect of all these mediums. It can show animated images and create graphic designs. The computer based learning is another gift of multimedia. Learning becomes easier and quicker when the text is supplemented with audiovisual assistance and for this reason it has become an effective mode of education for children as well as adults. The text on the screen is supported by audio instructions and visual aids which add to the grasping ability and memory retention of the students.

          All multimedia programs include six common elements - texts, pictures, movies, animation, sound and increased control. 

         Basing on the nature of interaction with the user, multimedia is divided into two types: Non-interactive and Interactive. In Non-interactive programs we simply receive information presented to us which are prepared in advance and processed by the computer with little or no intervention from the user. The images, sound and animation etc. are projected from the desktop directly onto the large screen, using a computer projection system or can be just seen on the computer screen. On the other hand, Interactive multimedia is meant for individual use that is, the user is in direct communication with the computer, receiving immediate responses to the input data. This type of multimedia usage is more common now-a-days.

          Multimedia requires storage of high quality images (graphics), texts, animations, sound, music and video for which high capacity storage medium is needed. The use of floppy disks is of no help though they are convenient to distribute. For this reason, multimedia information is usually stored in CD-ROMs (Compact Discs-Read Only Memory). A CD-ROM can contain upto 600 megabytes of data in it. For example, the entire Encyclopedia Britannica in all volumes can be stored in just one CD-ROM which can be carried in one’s pocket. 

            Compact disc is a new kind of disc which is recorded and played by laser beam. Compact disc has silvery, mirror-like surfaces which reflect light in a rainbow spectrum. The music disc is about 12 cm dia. while video disc is about the size of an LP and hold both pictures and sound.

            In the recording process, sound signals are converted into number so that each part of the signal has a precise code. These numbers are recorded as the binary digits 0 and 1. Physically, sound is recorded on a CD as a series of minute pits and flats which relate to the two digits.

           The laser disc has a very reflective metallic surface, covered by a protective coating of clear plastic. A semiconductor or small He-Ne laser is used for scanning. The player spins the disc and scans with laser beam which moves straight across the disc from the centre to the edge. The shiny surface reflects the beam back into the player, where it is picked up by electronic device. This produces an electrical signal which the player decodes back into video pictures and sounds. The laser beam reads about 20,000 digits every second which are converted into sound signals.

           The biggest advantage of compact discs is that they never wear out because there is no physical contact between the disc and the player - only a beam of light. 

Most large planes have an autopilot. This is a device operated by a computer. It will fly the plate without the pilot’s touching the controls. These autopilots can even control take offs and landings.

 

 

 

 

 

 

 

The principle of an automatic pilot is similar to the automatic steering of ships, but here three gyroscopic sensors and their associated equipment are used to control the three variables in aircraft position.

These three variables are yaw, pitch and roll. The complex autopilot system uses an airborne computer which activates servomotors for introducing necessary corrections. A radio or radar link to the computer allows control from the ground for automatic takeoffs and landings.

 

A bar code is computerized information encoded in a pattern of black and white stripes. The black and white lines represent IS and OS and can be read by light. They carry encoded information - from the membership number of a sports club to the price and stock number of a packet of washing powder in a supermarket. In fact bar codes are used to store data of all kinds.

The code is scanned by a beam of light. When a beam of light is passed over the bar code only the white stripes reflect back the light. This is picked up by a photo - detector which produces a pulse of electricity when it receives light. So the black and white bar code is translated into on/off pulses of electricity. These pulses are fed into a computer for decoding. Nowadays laser beams are being used for reading the bar codes.

          The remote control is a small hand-held device used by a viewer to control the television without touching its controls. It is an opto-electronic device which makes use of optical and electronic techniques and hardware.

           The remote control device emits a beam of light which is detected by a, “light control” built into the television. In an optical remote controller, a multivator (1) produces pulses (2) from push button controls (3). The pulses are amplified (4) and modulate a beam of light in the form of saw tooth pulses (5) These pulses are received by a photo transistor (6) fitted in the television set, amplified (7) and used as a trigger to recreate the pulse shape (8) The resulting signals are used to change volume and channels.

          The volume, contrast and channel can be altered by remote control. If the television is connected to a video cassette recorder, programmes can be recorded and replayed by remote control. A remote control prevents the wear and tear of switch buttons. 

              Scientists have developed the devices by which a door can be opened or closed automatically. There are three common ways of operating automatic doors: (1) by actuating a pressure pad on the surface in front of the door, (2) by cutting a light beam located in a wall near the door and (3) by actuating a wall mounted manual pressure pad like a switch.

              Automatic doors are powered by various drive systems - some are totally electric, some are electromechanical and others are pneumatic. Various door opening actions are available such as automatic slide with or without manual swing out side panels for use when the automatic doors are locked or turned off; single or double swing doors and side and swing combinations. Automatic door opening and closing devices are becoming more and more popular day by day. 

           Cellular telephone or radio telephone is a type of mobile telephone which is integrated with existing telephone systems, allowing mobile users to contact any one with a standard telephone and vice-versa. Each mobile telephone has its own number which can be dialed from any other telephone. The cellular telephone can cover the entire country; even inter-continental telephone calls are possible with cellular telephone.

           A cellular telephone network is setup by dividing the country into a series of cells, each with its own radio transmitter controlled by a central switching computer. Each cell is about 5km across and it broadcasts and receives low power signals on its own set of frequencies. Since each cell is so small, the same set of frequencies can be reused in any other cell whose transmitter’s range does not overlap the first cell. As a cellular telephone is mobile and moves from one cell to another, the broadcast frequency needs to be changed.

            Cellular radio phone signals follow a route starting from the mobile, then of the radio transmitter. The signal is sent along the conventional telephone lines to an exchange. The analog signal is converted to digital signal, ready for switching to the correct destination. After switching, the signal is reconverted to analog and sent along telephone lines to the destination transmitter, where it is transmitted and consequently received by another mobile.

           There are at present three types of cellular telephones. These are - automobile based, pocket or briefcase portables and trans-portables which can be moved in a vehicle and used in the hand.

           Cellular phones are being used by many countries besides India such as Saudi Arabia, U.S.A., Sweden, Britain, Japan, Middle East countries etc. 

          Star television is the popular name of satellite television. A broadcasting transmitter on the ground can transmit signals only to a limited distance. Even if the transmitting antenna is on a tall mast, hills and valleys in the landscape can soon block the signals. The television satellite can be taken as an antenna on an incredibly tall mast - so tall that it is in space.

          Satellites are being used for many years by TV stations to exchange TV programmes among each other. The signals are beamed out from earth station to spaces which are picked up by the aerial of the satellite. These signals are re-transmitted by the satellite down to another part of the earth where they are received by the dish antenna. The receiving TV station then transmits the signals to viewers in the usual way. In this way, TV signals are sent from one part of the world to the other. TV transmission from one earth station to the satellite and back to another earth station. Sports events are transmitted in this way.

          The latest development is direct broadcasting by satellite, known as D.S.B., where the signals go straight to the viewers. For this, you need a special dish aerial like the one shown here to pick up D.S.B. TV.