The function of an earth satellite station is to transmit and receive information frequency through microwave signals of a certain frequency. It has a large parabolic disc aerial. A communication satellite will amplify these microwave signals, convert them to another frequency and transmit them to other earth satellite stations. As the world becomes more sophisticated more modern communication methods and devices are introduced to the market.
Telegraph: a) the first telegraph was invented by George Lesage in 1774 b) A telegraph transmits signals by cable or radio waves c) the information is sent along a signal wire as pulses of electric current d) Each letter of the alphabet or digit is represented by a different code of pulses e) in 1837, an American inventor, Samuel Morse, revised a standardized telegraph code known as the Morse code that eventually made possible the development of the electric telegraph throughout the world f) the Morse code uses dots and dashes to represent alphabets and numbers g) The weakness of the telegraph is that it cannot send symbols or pictures h) The telegraph lasted until the 1950s when international telephone links were established.
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Telephone: a) the telephone was invented by Alexander Graham Bell in 1876 b) the telephone transmits speech in the form of electrical signals c) the mouthpiece of the telephone has a tiny carbon microphone which will change sound waves into electrical signals d) the earpiece of the telephone has a tiny loudspeaker which changes electrical signals to the sound of the caller’s speech e) Conversation through telephone is transmitted through i) metal telephone lines ii) fiber optics iii) ultra high frequency radio waves to transmission disc or receiver disc on a telephone tower iv) microwaves to the satellite f) Metal telephone lines are slowly being replaced by fiber optics because fiber optics: can carry more telephone calls, have less interference during transmission and are cheaper to produce.
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Facsimile Transmission or Fax: a) facsimile transmission or fax is a system of sending information on paper through telephone lines b) A facsimile or fax machine transmits a copy of the document itself c) it can therefore transmit pictures d)the documents is scanned and the image is converted into electrical signals e) when the signals arrive at the telephone receiver of the fax machine, the signals are separated from the carrier wave or decoded and fed into the printer f) the printer prints out a copy of the original documents.
Radio: a) the first person to develop practical radio equipment was Guglielmo Marconi b) information in the form of sound is transmitted from the transmitter to the receiver and it cannot transmit pictures c) radios transmit information with long waves, medium waves, short waves or very high frequency radio waves.
Television: a) the television is a system used to broadcast moving pictures and sound by radio waves b) video signals from a TV camera and sound signals from a microphone are modulated with carrier waves before they are transmitted c) these are picked up the receiver’s TV aerial, demodulated and amplified to work the picture tube and loudspeaker of the TV set
Computer: Computers are used to store and process data b) nowadays, a personal computer is used in communication through the Internet c) The Internet surfer needs to connect a modem to the computer d) the modem changes the information in the form of digital code to electrical signals before transmitting it through telephones lines e) the modem on the receiver computer will change the electrical signals back to digital code and display the information on the screen.
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Modern Communication Methods and Devices
As the world becomes more sophisticated more modern communication methods and devices are introduced to the market. Since the 1960s, satellites are used microwaves to relay information around the world. Most present day communication devices depend on satellites to transmit or receive information. Fiber optics was developed in the 1960s. They are capable of carrying many different types of communication via the same cable. The information is transmitted through a beam of light reflected along the insides of the cable.
With the introduction of the digital telephone, analogue signals were replaced by digital signals in the form of electrical pulses. The pulses produce a series of digits in binary code. The series of digits represent any form of information including speech, music, pictures and printed text. Digital signals are less likely to be distorted compared to analogue signals.
GPRS, MMS, WAP and VoIP
Present day hand phones are equipped with features that have more functions. Other than a camera and color display, digital music player and down-loadable ring-tones, more advanced hand phones are equipped with features such as GPRS, MMS, WAP and VoIP: a) GPRS or Global Positioning Remote Sensing enables us to locate the position of an object through the hand phone b) MMS or Multimedia Message Service enables us to use the hand phone to send pictures. We can see the receiver while talking using the headphone c) WAP or Wireless Application Protocol enables us to surf the Internet through the hand phone.
LCDs or Plasma Television
CRT televisions are slowly being replaced by flat panel LCDs or plasma televisions. A more flat screen will reduce the distortion of images. Teletext services through televisions provide current information on share prices and commodities, the money exchange rate and others.
Personal Digital Assistant (PDA) and Personal Computers
A PDA or Personal Digital Assistant is able to perform instant messaging between computers.
Modern day personal computers are able to perform more functions through the Internet: a) VoIP or Voice over Internet Protocol enables voice calls to be transmitted through the Internet b) we can communicate with people through the ICQ or MSN program c) on-line transactions can be carried out d) e-mails can also be used to send documents e) information can be obtained through web sites.
Communication satellites are geosynchronous satellites because they orbit at the same speed and at the same direction as the Earth’s rotation.
Radio astronomy uses large dish aerials called radio telescopes to pick up weal radio signals from distant stars and galaxies.
The lowest frequency which can be heard by humans is about 20 Hz and the highest is about 20,000 Hz but it varies according to individuals.