3l Satellite communications systems

GPS
1. Applications
  1. SatNav
    1. Offers maps, directions and warnings ETC
  2. GeoCaching
  3. GeoTagging
2. How it works
  1. 24 satellites in NAVSTAR constellation.
  2. Always at least 4 satellites in line of sight
    1. Uses 3 satellites to do trilateration, using distance from each station
  3. Orbit earth twice a year
3. Advantages
  1. O- No need for large maps
  2. O- Time saved planning journeys
  3. O- Calculates new route if error is made
  4. O- very accurate (as good as +- 30cm)
  5. O- Maps can be updated via internet
  6. O- GPS on phone can be used to find lost people
4. Disadvantages
  1. X- Blind-spots due to tunnels or building
  2. X- Maps may not up-to-date
  3. X- Atmospheric conditions can affect accuracy of GPS
  4. X- Drivers may become lost if GPS breaksdown
  5. X- Desired destination may not be recognised
  6. X- Setting destination and looking at SatNav may distract from driving
Weather
1. Applications
  1. Monitor cloud formations to predict direction of weather fronts
  2. Collect data on snow ad ice cover, pollution effects, fires, smog, dust and ocean currents
2. How it works
  1. Can have geostationary orbit 35,000 km over one spot on the equator
    1. Used by TV companies to provide cloud formation photos
  2. Polar orbit, orbits over the poles 850km above earth
    1. Higher quality pictures
    2. Can use thermal and infrared images to find land and water temperatures
3. Advantages
  1. O- Can monitor fires, hurricanes and sand clouds to give warnings
  2. O- Can track energy usage and light pollution
4. Disadvantages
  1. X- Expensive to build and launch satellites
  2. X- Weather forecasts may not always be accurate
  3. X- Concern over use of equipment for spying
Television
1. Applications
  1. Can watch more channels than with aerial due to high bandwidth
  2. Can be free to air or subscription
  3. Can be used with set top box to see TV guide
2. How it works
  1. TV companies send signals fro earth to a geosychronous satellite
    1. Direct Broadcast satellite (DBS) encrypt signal so homes can only receive channels they have paid for
      1. Signal compressed so more channels can be broadcast with same frequency
        Satellite dish receives microwave signals from space
        Receicer, set top box, decodes and decrypts signals to receive subscribed channels and decompress signal to find individual channel
3. Advantages
  1. O- High bandwidth=> Hundreds of channels available
  2. O- Can be received in remote areas where antenna signal is weak
  3. O- Encrypted signals so viewers can pay for one-off programmes or subscriptins
4. Disadvantages
  1. X- Equipment/ subscription is initially expensive
  2. X- Need extra set top boxes to have satellite TV in other rooms
  3. X- Weather conditions affects satellite signal
  4. X- Signal dish is unsightly

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3l Satellite communications systems

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	Criado por Gladys Mba mais de 7 anos atrás