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Am and Fm radio

  1. Apr 17, 2009 #1


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    Hey all

    I have to do a massive physics report on the topic "a comparison of Am against FM broadcasting."

    What are some topics i could research and compare.

  2. jcsd
  3. Apr 17, 2009 #2


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    Gold Member

    Welcome to PF, HVC.
    One main thing that you should look into is how the RF waves propagate. There is a difference as to how they interact with the ionosphere.
  4. Apr 18, 2009 #3
    What level of physics is this for?

    Regardless of that, the differences in their frequency bands and the different methods with which the two transmit data in should be main topics.
  5. Apr 18, 2009 #4


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    its for grade 12

    so far ive got
    the way they are differently modulated
    how the modulations have their benefits and cons
    and a bit on propagation

    anything else important?
  6. Apr 18, 2009 #5
    Other subjects might be
    Broadcast range (night and day); attenuation in air
    [I remember as a kid living in California and picking up AM stations in Texas and Pennsylvania at night]
    (ionospheric effects mentioned above)
    channel bandwidth; mono and stereo broadcasts
    Use of vestigal sidebands (in FM) (carriers above audio in FM channel bandwidth)
    Signal to noise (AM and FM) and bit error rate (in digital broadcasts)
    Inherent benefit of FM over AM (noise rejection) (comparison of upper and lower sidebands)
    Noise figures (kTB) of receivers at 1 MHz (AM) and 100 MHz (FM)
    [kTB = Boltzmann's constant times temperature times bandwidth]
    Zero power AM receivers (I built a crystal radio receiver about 1947)
  7. Apr 18, 2009 #6


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    Homework Helper

    As mentioned, it's mostly due to frequency differences in commercial AM versus FM broadcast. As I understand it, HAM radio operators can choose to use AM or FM on selected frequencies that range from 1.8 mhz to 275 ghz. The other differnce is that with AM radio the strength of the signal varies with amplitude, the sound wave is represented by the change in amplitude of an AM broadcast. In FM, the amplitude is constant, and the sound wave amplitude is represented as a deviation in frequency from the main frequency. For stereo, a pair of frequencies is used.

    The lower frequency AM radio stations can bounce off the upper atmosphere, especially at night. In the days when AM radio was popular for music, KOMA, at 50,000 watts, in Oklahoma could be heard just about anywhere not blocked by the Rocky Mountanins to the west. XERB, with a 50,000 watt transmitter "aimed" northward from Mexico, (studio was in Las Vegas, remember Wolf Man Jack?), could be heard just about anywhere in California.

    Low frequency, low power, HAM radio signals can be receiived cross continent occasionally.
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