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Radio stations

Discussion in 'General Electronics' started by KellyClarksonTV, Nov 7, 2004.

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  1. Recently my grandma (from Taiwan) gave me a radio that tunes into channels in
    the 70MHz-108MHz range, so I was playing around with the lower channels most of
    us are not familiar with, but I did happen to hear some familiar voices from
    regular (88-108) channels ... Do they broadcast to these stations, or could it
    be someone (perhaps a neighbor) rebroadcasted them for some reason? If anyone
    has a similar radio, please try it out yourself.
     
  2. Karl Uppiano

    Karl Uppiano Guest

    In the US, the FM band is sandwiched between TV channels 6 & 7. If you tune
    down to the low end of the FM band, you'll hear channel 6 audio. If you have
    a radio that allows you to keep tuning down, you should get a bunch of noise
    that would be channel 6 video. Below that is channel 5 audio, followed by
    channel 5 video. The range from 76 down to 72 MHz is fixed and mobile
    communication, aeronautical radio navigation and radio astronomy. These
    services might show up as noise (they're probably not broadcasting audio
    signals). The mobile services are probably AM or narrow-band FM two-way
    voice. The only thing that would sound like normal radio programming would
    be the TV audio, AFAIK.

    If you're hearing actual replicas of stations from the standard FM band,
    it's possible that the radio is suffering from "images", the result of
    front-end overload, or some other artifact of the frequency conversion
    process that goes on in superhet radios. For example, the intermediate
    frequency of most FM receivers is 10.7 MHz, so it's possible that a nearby
    radio that was tuned in to a station in the standard band could re-radiate
    (or fool your radio into receiving) the station on a frequency 10.7 MHz
    below the regular assigned frequency.

    Here's a chart showing the US radio spectrum allocation:
    http://www.ntia.doc.gov/osmhome/allochrt.pdf
     
  3. Thanks. I do hear channel 6 audio now. However, I'm also hearing 100.7FM in the
    sub-88 range, far less than just 10.7MHz off. Any other explanation of this?
     
  4. Karl Uppiano

    Karl Uppiano Guest

    Hmmm... 100.7 - 10.7 = 90, doesn't add up, however, 100.7 - (10.7 * 2) =
    79.3, which might be in range. Also, not all receivers use a 10.7 MHz IF. I
    might be grasping at straws here, though. If the experimental data doesn't
    match the model, the model might be in error.
     
  5. Joe

    Joe Guest

    Another consideration is the calibration of your radio dial along with your
    interpetation of the dial. Even an inexpensive radio with digital dials can
    be off 0.2 or more.
     
  6. Hey guys, you should really get a radio with 70-88MHz range ... there's two
    X-rated stations in this range in our area ... for real ...
     
  7. Karl Uppiano

    Karl Uppiano Guest

    OK, that would have to be the neighbor kid with a homebrew transmitter, but
    why they would be broadcasting to basically no-one is beyond me. Besides, no
    commercial station would risk their license like that.

    Unless... Your area is not in the continental United States...
     
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