The VSWR meter measures the standing wave (a single-frequency mode of vibration of a body or physical system in which the amplitude varies from place to place) ratio in a transmission line in order to check the quality of radio equipment. The meter refers to the match between the antenna and the transmission line. A VSWR meter should be installed near the antenna to avoid loss of transmission, which happens because transmission lines have a certain amount of loss. The reflected power travels back to the cable, producing a low reading on a VSWR meter.
Definition
"VSWR" stands for "Voltage Standing Wave Ratio." It is an RF (radio frequency) signal source, a coaxial cable (i.e., a transmission line that consists of a tube of electrically conducting material surrounding a central conductor held in place by insulators) with some sort of mechanism to allow access to the center conductor at various lengths, load impedance for the other end of the coaxial cable, and some kind of meter to be able to measure the RF voltage as a probe selecting various points along the coaxial cable. The VSWR is a measure of impendence mismatch between the transmission line and its load. A transmission line can be defined as a device which transmits or leads energy from one point to another. The desired outcome is the highest efficiency. The intention is to diminish the loss through heat and radiation at its maximum.
Signal Source
The voltage component of a standing wave in a transmission line consists of forward wave superimposed on the reflected wave. The signal source is generally set to a fixed frequency and is tuned up for a good output voltage.
Ideal System
An ideal system would transmit energy without any loss along the way. This requires an exact match between the source impedance, the characteristic impedance of the transmission line and all its connectors as well as the load's impedance. The signal's AC (alternate current) voltage will be the same from end to end since it runs through without interference.
Real Systems
Mismatched impedances in real systems cause some reflection of the power toward the source, a kind of "echo" effect. These reflections end up as destructive interference, resulting in the rise and fall of the voltage at various times and distances along the line. A VSWR meter measures these voltage differences.
Tags: transmission line, coaxial cable, VSWR meter, line VSWR, line VSWR meter
