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Homework Help: Physics in TV's

  1. Mar 10, 2010 #1
    1. The problem statement, all variables and given/known data

    I was given these two questions to answer regarding TV:
    1) Explain why there is a need for two sound carrier frequencies.
    2)Explain why you still get good sound quality reception during a thunderstorm but picture quality declines.

    2. Relevant equations
    I was given this information within the question

    Australian TV broadcast standards:
    Vision Carrier - 1.25 MHz above lower edge of channel
    Vision Modulation - negative AM
    Lines per picture - 625 interlaced 2:1
    Line freqeuncy - 15625 Hz
    Primary Sound Carrier - 5.5MHz above vision carrier
    Secondary sound carrier - 242.1875kHz above primary sound carrier
    sound modulation - FM

    3. The attempt at a solution

    1) The only thing I can think is so two sound waves can be played at the one time. For example: like having a person speaking with background music playing also.

    2)I think it has something to do with picture being AM and sound being FM. I know that AM modulation is susceptible to noise. FM has less noise as a limiting circuit keepts the amplitude a near constant. The noise could explain the decline in sound quality reception...

    I'm pretty stuck here. Any help would be greatly appreciated.
  2. jcsd
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