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Thread: Why didn't FCC allow FM on 27Mhz CB?

  1. #1

    Why didn't FCC allow FM on 27Mhz CB?

    I've got no idea what the audience size is in this little corner of the forum, but what the heck...


    Why didn't FCC allow FM on 27Mhz CB? My suspicion would be primarily interoperability issues with the millions of other transceivers out in the market at the time.

    Of course, an AM/FM switch would have eliminated that as an issue...but, a few European countries allowed FM by the late 1970's, didn't they?

    Any places I should go root around to find some history on the topic?

    Thanx!

  2. #2

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    FM only sounds good above the level of full quieting.
    Below that level, it becomes progressively noisier.
    A better alternative is SSB, which is available in many radios.
    SSB has the best range with the least signal and uses the narrowest bandwidth.
    What more can anyone ask for.
    Ai4i has Always Been on the Trailing Edge of Technology!

  3. #3
    Quote Originally Posted by ai4i View Post
    FM only sounds good above the level of full quieting.
    Below that level, it becomes progressively noisier.
    A better alternative is SSB, which is available in many radios.
    SSB has the best range with the least signal and uses the narrowest bandwidth.
    What more can anyone ask for.
    FM is used on repeaters in the 10-meter amateur band, just above the CB range.

  4. #4

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    Quote Originally Posted by CTListener View Post
    FM is used on repeaters in the 10-meter amateur band, just above the CB range.
    Only as an "exotic" mode with all kinds of propagational issues.

  5. #5
    I think it mainly boils down to the bandwidth. In theory, the deviation could be small, but in reality, to produce that waveform, a much wider bandwidth of spurs, like harmonic sidebands required to reproduce accurately high fidelity audio like a voice or musical instrument, is required. It's in the ARRL Book "FM And Repeaters". In Mathematics, it's Fourier Analysis applied to an FM Waveform. Does this make any sense to you? I know I was confused until I took Advanced Calculus and read that ARRL book. The guy from the UM Amateur Club thought I was unsophisticated for asking.
    Last edited by Schroedingers Cat; 12-06-2018 at 10:22 PM.

  6. #6
    Apologies for the delay in a response...

    Yes, the technical perspective is helpful, and perhaps ties into the legal perspective of why it was never considered. Yet, Europe did require its use (maybe not all of the continent, but a percentage did), but that was so there wouldn't be those technical issues with propagation (e.g. prevent skip-shooting between the US and the UK...)

    One would have seriously though that during the period when 23 channel units were being considered for sale in 1977, FM may have also entered into the discussion.

  7. #7
    AM at a min travels 50% further that is why FM was never allowed on CB. AM does not sound that bad really with a nice radio and a good microphone.
    Phat Beats Radio playing the best Rap Hiphop R&B Soul Funk from the 1970s to early 2000s http://phatbeatsradio.com

  8. #8
    Yet, it was the intention in the early, early days for CB to be a poor-man's business radio of sorts. Low-power meant local communications (mainly...) so the "travels further" would have seemed to have worked in favor of the low-power, short-distance communications medium.

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