P1 Revision Cards- Wireless Signals

P1 revision cards for wireless signals

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  • Created by: Eleanor.1
  • Created on: 22-04-14 17:29

Radio Refraction and Interferance

  • Wireless technology is used by:
    • radio and television
    • laptops
    • mobile phones
  • Radio waves are reflected and refracted in the Earth's atmosphere:
    • The amount of refraction depends on the frequency of the wave.
    • There is less refraction at higher frequencies.
  • Radio stations broadcast signas with a particular frequency.
  • The same frequency can be used by more than one radio station:
    • The radio stations are too far away from each other to interfere.
    • But in unusual weather conditions, the radio waves can travel futher, and the radio waves can interfere.
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Radio Refraction and Interferance 2

Interferance is reduced if digital signals are used.

  • Digital Audio Broadcasting (DAB) also provides a greater choice of radio stations but the audio quatlity isn't as good as the FM signals currently used.
  • DAB eliminates interferance between other radio stations.
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Radio Reflection

  • Radio waves are reflected from ionosphere. They behave like light in an optical fibre and undergo total internal reflection.
    • Ionosphere- a region of the Earth's atmosphere where ionisation caused by incoming solar affects the transmission of radio waves; it extends from 70km to 400km above the Earth's surface.
    • Ionisation- The formulation of ions (charged particles).
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Radio Refection 2

  • Water reflects radio waves but land mass does not.
  • Continued reflection by the ionosphere and the oceans allow radio waves to be recieved from an aerial that is not the line of sight.
  • Microwaves pass through the ionosphere.
  • Microwave signals are recieved by orbiting satellites, amplified and retransmitting back to Earth.
  • Communication satellites orbit above the equatorand take 24 hours to orbit Earth.
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Communication Problems

  • Radio waves are diffracted when they meet an obstruction.
  • Refraction in the atmosphere needs to be taken into account when sending a signal to a satellite.
  • The transmitting aerial needs to send a focused beam to the satellite because its aerial is very small.
  • The transmitted beam is slightly divergant.
  • Some energy is lost from the edge of the transmitting aerial becuse of diffraction.
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