Answer to Question #87655 in Optics for Shivam Nishad

Question

Explain how signal losses and noise is reduced in case of twisted pair and coaxial
cables

Answer 1

Noises are generated in signal lines by magnetic fields from the environment. So the noise current in data lines is the result of that magnetic field. In the straight cable, all noise current is flowing in the same direction, just like in an ordinary transformer coil. When the cable is twisted, in some parts of the signal lines the direction of the noise current is the opposite from the current in other parts of the cable. Twisting decreases the cross-talk interference between adjacent pairs in a cable. That is, each twist of the lines generates a loop, where the current generated from external fields coming from the source and returning from the load will "rotate" in an opposed sense to that in the next loop. Thus, the contribution of each loop cancels the other (more or less). Thus, the influence of external magnetic fields is greatly reduced.