Topic 11- Communications
11.4 – Channels of Communication
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.
Types of Cable
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.
Coaxial Cables
• Made up of two conductors surrounded by a
sheath.
• Much less attenuation in coaxial cables.
• Has a longer range than wire pairs.
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.
Satellite Communication
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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?
The Internet
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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:
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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:
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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.