Analysis of the induced voltage on a twisted pair cable in an electromagnetic field

Abstract

A method for estimating the induced voltage on a communication cable consisting of a twisted pair cable in electromagnetic field is proposed. The analysis proposed here is based on the reciprocity theorem in antenna technology. First, a radio frequency source is connected to the communication cable as a transmitting antenna. The cable radiates an electromagnetic field. The induced open voltage at the terminal of the half-wavelength dipole as a receiving antenna is then analyzed. From the reciprocal theorem, the induced voltage on the dipole is equal to the induced voltage on the cable. The parallel and cross components of the electric field radiated from a distribution circuit are calculated. The analysis takes into account the current of even and odd modes on the cable. The loss caused by materials in the cable is also taken into account for practical cable analysis. From the results of experiments at a frequency of 300 MHz, it is confirmed that the radiation field from the pair cable can be estimated quantitatively by using the proposed analysis. The induced voltage on a cable having a length of 100 m in an electromagnetic field is estimated by using this method. It is noticed that the induced voltage is strongly increased when the cable has an unbalanced component (i.e., the even mode). © 1999 Scripta Technica, Electron Comm Jpn Pt 1, 82(11): 32–44, 1999