Insertion Loss in Coaxial Transmission Lines from Impedance Mismatches

摘要

The objective of this paper is to provide CATV cable professionals with an uncomplicated understanding of the relationship between impedance variations and signal loss in coaxial cable transmission lines. Impedance discontinuities whether quantified as a change in impedance in Ohms, reflection coefficient, return loss or voltage standing wave ratio (VSWR), have an effect resulting in loss to a propagating signal. This loss is known as reflection loss. CATV networks use low power compared to 50 Ohm transmission line systems and for this reason this paper only focuses on the signal loss characteristic and not reflected power. A basic and useful understanding of the relationship between impedance change and signal loss and a technique to quantify the corresponding amount of signal loss in dB (decibel) will help cable professionals better understand and predict cable system performance. Data from laboratory testing to-support the theoretical principles-of signal loss from impedance change is included in this paper. Since signal loss is often described as attenuation or insertion loss, these terms will be defined and must be -understood to enable comprehension of this topic.