What does an SWR meter measure?

An SWR meter measures the Standing Wave Ratio, which is a crucial parameter in understanding how effectively a radio frequency (RF) transmission line is functioning. The Standing Wave Ratio indicates the balance between the forward and reflected power in a transmission line. In an ideal system where all the power is transmitted to the antenna and none is reflected back, the SWR would be 1:1.

When the ratio is higher, it suggests that some of the transmitted power is being reflected back towards the source due to impedance mismatches. This can lead to inefficiencies in the system and potentially damage the transmitter if the SWR is too high. Understanding and measuring the SWR allows operators to diagnose issues in the antenna system, ensure optimal performance, and make necessary adjustments to improve transmission quality.

The other options, while related to radio frequency measurements, do not specifically describe what the SWR meter is designed to measure. For instance, voltage reflection, signal distortion, and power output are relevant but do not directly define the purpose of an SWR meter. The primary function of the SWR meter is to provide a direct measurement of the standing wave ratio on the transmission line, making option D the accurate choice.