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Why is Electrical length greater than physical length?

Discussion in 'General Electronics Discussion' started by shopitham, Feb 14, 2011.

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  1. shopitham

    shopitham

    5
    0
    Nov 30, 2010
    HTML:
    Hai
    1)What does a electrical length in transmission line means?
    2)How does it differ from the physical length?
    3)Why is electrical greater than that of the physical length?
    some pls help me find the ans .
    
    Thanks
    Shofiya
    
     
  2. rob_croxford

    rob_croxford

    262
    0
    Aug 3, 2010
    The Physical length of a coaxial cable (such as cable used in transmission lines) is the length from one end of the connector to the other.

    The ELECTRICAL length of such a cable depends on the size and type of the dialectric material used within it (if im not mistaken). It is measured at the mating plane of the outer conductor and is the length of the adapter as it appears to the signal traveling through it.

    Try google if u need more info.

    Rob
     
  3. davenn

    davenn Moderator

    13,785
    1,936
    Sep 5, 2009
    The electrical length of a transmission line is dependant on 2 things...

    1 ... the velocity factor of the line and
    2 ... the frequency
    an example ... to find the electrical length of a transmission line or dipole antenna
    say for 400MHz

    (300 million metres / sec (300,000 km / sec))
    300 / 400MHz = 0.75m or 75cm that is the wavelength
    now if we want an electrical wavelength in a transmission line that has a VF (velocity Factor) of 0.85 then....

    75 x 0.85 = 63.75 cm so you can see that the electrical wavelength is shorter
    than the free space wavelength

    Dave

    Dave
     
  4. ans

    ans

    19
    0
    Nov 25, 2010
    Nice information thanks for sharing.
     
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