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Telephone loading coils

  1. Apr 10, 2008 #1
    how do they improve high-frequency transmission (and not low-frequency?) ?

    I'm a biologist...

  2. jcsd
  3. Apr 18, 2008 #2
    I have a Robert Chipman book on transmission lines that mentioned this issue. As I recall, the loading coils did not improve high frequency transmission, but rather, just the opposite. The loading coils were removed for that reason.

    I'll check my reference when I get home tonight, but I seem to remember that the reason for adding the loading coils was to lower distortion. Sir Oliver Heaviside determined in the 19th century that distortionles transmission takes place when R/L = G/C, where R, L, G, & C are the transmission line series resistance, inductance, shunt conductance, & capacitance per unit length resp.

    The loading coils make it easy to optimize the ratio to get low distortion. They were added around 1925. But they acted as a low pass filter, attenuating hf response. They were removed around 1940. From memory, that is what I recall. At home I'll check the reference material and post a correction if needed. BR.

  4. Apr 18, 2008 #3


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    Staff: Mentor

    What's a telephone loading coil?
  5. Apr 21, 2008 #4
    thanks cabraham.

    berkeman, it beats me - this is why I asked :S
  6. Apr 21, 2008 #5

    Used to improve the transmission line for speech.


    I wonder if they were those little bobbin things I used to see in telephone lines in my dim & distant youth... I always wondered what they were for...
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