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Cable gain

Discussion in 'General Electronics Discussion' started by samurai14, Apr 3, 2010.

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  1. samurai14

    samurai14

    1
    0
    Apr 3, 2010
    Hi, I have a question, what is the formula to work out the output W of a cable with 2W input and a 13dB gain......please please help....
     
  2. (*steve*)

    (*steve*) ¡sǝpodᴉʇuɐ ǝɥʇ ɹɐǝɥd Moderator

    25,497
    2,839
    Jan 21, 2010
    A cable with gain?
     
  3. davenn

    davenn Moderator

    13,866
    1,958
    Sep 5, 2009
    hahaha

    dang thats what we all need huh steve ;)

    we could do away with expensive amplifiers then

    samurai14

    cables DO NOT, NEVER EVER have gain, they only have losses and the longer
    the length and/or the higher the frequency used the greater the losses are

    The loss is usually expressed in dB / metre or if you are in the USA dB / foot
    or some variation of eg at 1000MHz (1GHz) a given cable mite have a loss of
    12dB / 30 metres (100ft) a much better quality cable may only have a loss of
    8dB / 30m at 1GHz

    in your case we need more information as well ....
    you have told us you are putting 2W into one end of the cable, we need to know at what frequency ??
    and we need to know what cable type and its length ?? so we can look
    up its specifications and find its losses at that freq and length.
    Lets for example sake say it has 3dB loss for 10metres at your frequency of 400MHz
    then you will have only 1W at the far end of the cable... 3dB loss represents 1/2 the
    power lost

    Now I have assumed you have been talking about an RF signal into say a coaxial cable
    (thats what I mainly deal with)
    but it doesnt really matter even if it is an audio signal into a long twin wire (figure 8) speaker
    lead. there will still be losses, just a lot smaller

    cheers
    Dave
    VK2TDN
     
    Last edited: Apr 4, 2010
  4. neon

    neon

    1,325
    0
    Oct 21, 2006
    cables do not have any gains ever only losses. importance is the cable lenght for cable frequency transmission . any cable must be cut at the right lenght for the right frequency otherwise it can show as virtual short.
     
  5. Resqueline

    Resqueline

    2,848
    2
    Jul 31, 2009
    As usual neon tells only half the story.. He's right only if the cable end is left open (or shorted). If it's properly terminated then length doesn't matter.
    If the cable is not terminated with the proper impedance then the cable input impedance will vary with frequency.

    But we are still in the dark here as to what the o/p actually had in mind..
     
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