How do Telephone Loading Coils Improve High-Frequency Transmission?

[garytse86]

how do they improve high-frequency transmission (and not low-frequency?) ?

I'm a biologist...

Thanks

 

[cabraham]

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.

Claude

 

[berkeman]

What's a telephone loading coil?

 

[garytse86]

thanks cabraham.

berkeman, it beats me - this is why I asked :S

 

[zeitghost]

http://en.wikipedia.org/wiki/Loading_coil

Used to improve the transmission line for speech.

Apparently.

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...