9.1.1

Communication Channels

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Transmission Media

Transmission media are different ways of physically transferring data from one place to another.

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Bandwidth

  • The bandwidth of a wave is the range of frequencies in the wave.
  • Bandwidth can also be thought of the amount of data that can be transferred in a given time.
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Twisted-pair copper cable

  • Inside the cable, there are eight wires which are twisted into pairs. This is to reduce interference from other signals and improve transmission speed.
  • Twisted cables have different ratings to indicate how quickly data can be transferred.
    • E.g. Cat-5e can transmit at 1 Gbps.
    • E.g. Cat-6 can transmit at 10 Gbps.
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Fibre-optic cable

  • Fibre-optic cables are made of thin strands of glass which transmit binary data as pulses of light.
  • Fibre-optic cables have many advantages:
    • Do not suffer interference.
    • Very high bandwidth (100Tbps).
  • Because of the lack of interference, fibre-optic cabling is appropriate for long distance communication such as undersea cabling.
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Radio waves

  • Radio waves are the transmission media of wireless networking.
    • E.g. WiFi.
    • E.g. Bluetooth.
  • The amplitude (strength) of a radio wave decreases as it moves further from its transmitter. This is why WiFi signal loses strength further away from a WAP.
  • Radio waves are also subject to interference from other radio signals of similar frequency. Wireless access points (WAPs) often check for frequency channels that are least congested before starting a broadcast.
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Coaxial cable

  • Coaxial cable is a wired transmission media where an insulated copper wire is surrounded by a metal mesh to protect it from interference.
    • This is most often used for cable television.

Satellites in Communication

Satellites allow us to transmit information over very large distances

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Geostationary satellites

  • A geostationary (or geosynchronous) satellite is one that always appears in the same place in the sky, no matter what the time of day. For this to happen, the satellite must:
    • Have an orbital period of exactly one day (23 hours 56 mins 4.09 secs).
    • Be in a circular orbit very near to the equator.
    • Be orbiting in the same direction as the Earth is rotating.
  • The geostationary orbit may be calculated to be 35 790 km above the Earth.
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Polar orbiting satellites

  • Polar orbiting satellites pass over the north and south poles of the Earth over the course of one orbital period.
  • Polar orbiting satellites tend to be approximately 800 km above the Earth.
    • This means they have an orbital period of approximately 100 minutes.
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Differences

  • Polar orbiting satellites experience less delay in communication times than geostationary satellites as their orbit is low.
  • Polar orbiting satellites scan the whole surface of the Earth, whereas geostationary satellites are tied to one location.
  • Aerials connected to geostationary satellites don't have to be moved as their position remains fixed in the sky.

Jump to other topics

1Physical Quantities & Units

2Measurement Techniques

3Kinematics

4Dynamics

5Gravitational Fields

6Deformation of Solids

7Thermal Physics

8Oscillations

9Communication

10Electric Fields

11Current Electricity

12Magnetic Fields

13Modern Physics

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