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  1. Member Frank-0-Video's Avatar
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    Jan 2009
    Alabama - United States
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    Greetings ...

    My basic understanding of coaxial cable - for the purposes of transmitting analog or digital channels - is that it has a capacity of at least 900 mhz (if not more). That would equate to 150 analog channels, or to 150 to 600 (if not more, and depending on conditions) digital channels.

    Now, with regards to Fiber-Optic Cable, are we truely talking about capacity in the GHZ range? If so, how many GHZ are we dealing with? It is a personal assumption that if in fiber-optic the capacity is at least 10 GHZ (10,000 mhz), then this would equate to 1,600+ analog channels, or to 1,600 to 6,400 digital channels.

    Please enlighten me - brief explanation will do.

    Thanx-A-Lot, Frank-0-Video
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  2. Member edDV's Avatar
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    Mar 2004
    Northern California, USA
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    The Cable standards used in North America allow up to 1GHz (~166 6MHz RF channels) although installed base is likely less (e.g. 550, 650, 750MHz) depending on latest upgrade. The bandwidth depends more on the electronic repeaters than coax itself. I'm on a recent Comcast upgrade that is fiber fed to the last mile or so. The highest current channel I've noticed is ~800 MHz (ch 124) but it may go higher. Each 6MHz channel can carry one analog channel or up to ~38Mb/s data (256QAM modulated).

    Typical US cable systems carry 70 or so analog NTSC channels. The rest carry internet up/down, telephone, VOD or MPeg2 digital subchannels. Each 6MHz QAM modulated channel can carry 8-10 SD or 1-3 HD MPeg2 subchannels or a combination.

    Fiber can carry greater bandwidth but in typical telco applications sends 10 to 40Gb/s of data per fiber strand. Much more is possible but in practice more fiber strands are used per cable to allow easier distribution. The type of fiber used for street or building distribution may carry less due to the need for shorter bending radius.

    So in practical use, coax using 256QAM on all channels could send ~ 6Gb/s. Fiber can send 40 to >100Gb/s per strand. The other main advantages for fiber are longer distance between repeaters and smaller diameter allowing many fiber strands per jacketed cable.
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