1. Channels of Communication SL – Option F.4

2. Ways of Communicating Wire Pairs –This is the cheapest form of cable, they are 2 insulated wires that are run together –When the wires are twisted together, the two signals (one in, one out) cancel out any EM interference from neighboring wires –Because they are thin, attenuation due to resistivity is larger Decent for short range networking

3. Ways of Communicating Coaxial Cable –Made up of a copper wire, surrounded by an insulator, surrounded by a conducting sheath, surrounded by an insulator Primarily used for TV signals and internet Copper sheath prevents attenuation from radiation and interference from outside signals

4. Ways of Communicating Optical Fiber –See F.3 notes –Advantages over Coax Great for transmitting digital data Higher bit rate Smaller Diameter Low Noise –Disadvantages Can be difficult to access and repair Amplifiers and reshapers have a finite life

5. Ways of Communicating Radio Waves –See F.1 notes –With radio signals, keep in mind that the signal is always analogue but it can transmit digital information –Advantage is that no wires are necessary to transmit data

6. Geostationary Satellites Orbit the Earth at the equator and has an orbital period of one sidereal day –Time it takes the Earth to make one complete rotation around its axis –This means that the satellite is always above the same geographic position on Earth –Altitude is about 3.6 x 10 7 m up –Currently there are 5 or 6 at different positions

7. Geostationary Satellites Used for more direct transmission of signals –One satellite can get a signal to where it would take many grounded antennas to get to –The frequencies range from.1 – 10 GHz Uplink and down link frequencies must be different to avoid interference and unwanted noise

8. Polar-Orbiting Satellites A satellite that is in orbit around the Earth in a N/S or S/N path. –The satellite passes over both poles in its orbit –Path is nearly normal to the equator –Not geosynchronous and so has a much lower altitude –Passes along a different longitude with each trip

9. Comparing Satellites Benefits of GS –always above the same position on Earth so there is no need for tracking –That location will always have access to the satellite Benefits of PS –Lower altitude so the signal doesn’t need as much power to transmit Also cheaper to put into orbit due to altitude –GS can’t transmit more than about 60-70 deg. N or S of the equator

10. Issues with Communication Moral, ethical, economic, environmental