1. Topic 11- Communications 11.4 – Channels of Communication

2. Learning Outcomes F.4.1 Outline different channels of communication, including wire pairs, coaxil cables, optic fibres, radio waves and satellite communication. F.4.2 Discuss the uses and the relative advantages and disadvantages of wire pairs, coaxil cables, optic fibres and radio waves F.4.3 State what is meant by a geostationary satellite. F.4.4 State the order of magnitude of the frequencies used for communication with geostationary satellites, and explain why the uplink frequency and the down-link frequency are different. F.4.5 Discuss the relative advantages and disadvantages of the use of geostationary and polar-orbiting satellites for communication. F.4.6 Discuss the moral, ethical, economic and environmental issues arising from satellite communication F.2.9 Discuss the moral, ethical and environmental issues arising from access to the internet.

3. Types of Cable

4. Wire Pairs Cheapest form of cable. Made up of two insulated wires. As length of cables increases, strength of signal decreases. – Attenuation Attenuation is caused by resistance which is dependent on the material used and by radiation loss. Attenuation increases with frequency so wire pairs can only be used with low frequencies.

5. Coaxial Cables Made up of two conductors surrounded by a sheath. Much less attenuation in coaxial cables. Has a longer range than wire pairs.

6. The use of Radio Waves Radio Waves: Continuous variation of electric and magnetic fields, thus, they are analogue signals. They can be used to transmit digital signals through wave modulation. Amplitude Modulation: The amplitude is modulated between two values. Frequency Modulation: The frequency of the carrier wave is modulated between two frequencies.

7. Satellite Communication The use of high frequency modulated radio waves to transmit digital information would be great, if not for the fact that the transmitter and receiver must be in a direct line of contact. Thus, in order to do this, a series of transmitters and receivers must be constructed. To overcome this problem, satellite communication is used. Geostationary Satellites: Satellite which are positioned above the equator and circles the earth at the same rate and have the same axis of rotation in order to make sure they are above the same point on earth. Satellite TV : Satellite TV stations use geostationary satellites for transmission. The signal is sent to the satellite with a certain uplink frequency and sent back down to earth with another to avoid interference between the two signals. The signal is then picked up with a parabolic dish and decoded with a receiver. Polar Satellites: Orbit the North and South Poles. Much lower orbit than geostationary satellites and move faster. Communication in Remote Areas: Since satellites are unaffected by natural disasters, they can be used to communicate with inaccessible areas of the earth after such events. International Understanding: Since satellites do not lie within national boundaries, satellites give many possibilities for cross cultural exchange. Viewers can watch news programs with a new perspective. International communication leads to international understanding. Environmental Concerns: To place a satellite into space there needs to be fuel and launch pads; however, they also reduce the needs to build transmitters or lay cables. Colonization of Space: Who owns space? Can anyone take over a piece of space for their satellite?

8. The Internet Through the internet, computer can communicate with all other computers which are connected. Using the internet, data can be sent in packets, disassembled, and reassembled at the receiver. Advantages: – Can communicate with many people at once – Information can be shared easily using web pages and social networking – Internet is great for business as people can sell and buy things over the internet Disadvantages: – Copyright infringement: Music and video can be shared illegally over the internet – Pornography: In some countries, pornography is illegal; however, due to the internet, it can be accessed everywhere. – People with extreme views can communicate with others with equally extreme views – Gambling can take place over the internet with no regulation and no control. – Plagiarism has become more common since the creation of the internet due to the sharing of information. – Spam: The ability to send an email to millions of people at the same time has been abused.