P1g: Wireless Signals

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Mind Map on P1g: Wireless Signals, created by antonia_f on 06/26/2014.
antonia_f
Mind Map by antonia_f, updated more than 1 year ago
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Created by antonia_f over 10 years ago
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Resource summary

P1g: Wireless Signals
  1. Radio Refraction and Interference
    1. 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
      1. Radio stations broadcast signals with a particular frequency
        1. 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 further and the broadcasts interfere.
          1. Interference is reduced if digital signals are used.
            1. Wireless technology is used by: ––radio and television ––laptops
              1. Digital Audio Broadcasting or DAB also provides a greater choice of radio stations but the audio quality is not as good as the FM signals currently used.
                1. DAB eliminates interference between other radio stations
                2. Radio Reflection
                  1. Radio waves are reflected from the ionosphere. They behave like light in an optical fibre and undergo total internal reflection.
                    1. Microwaves pass through the ionosphere.
                      1. Communication satellites orbit above the equator and take 24 hours to orbit Earth
                        1. Water reflects radio waves but land mass does not.
                          1. Continued reflection by the ionosphere and the oceans allows radio waves to be received from an aerial that is not in line of sight.
                            1. Microwave signals are received by orbiting satellites, amplified and retransmitted back to Earth.
                            2. Communication Problems
                              1. The transmitting aerial needs to send a focused beam to the satellite because its aerial is very small.
                                1. The transmitted beam is slightly divergent.
                                  1. Some energy is lost from the edge of the transmitting aerial because of diffraction
                                    1. Radio waves are diffracted when they meet an obstruction
                                      1. Refraction in the atmosphere needs to be taken into account when sending a signal to a satellite.
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