What does an S meter measure?

An 'S meter' stands for 'Signal meter,' which is a visual indicator on a receiver's front panel used to display the relative strength of incoming radio frequency (RF) signals. The scale is typically calibrated in 'S units' from S1 (very weak) to S9 (very strong), with an extended decibel (dB) scale for signals that exceed S9. Distractors like 'Transmitter power output' are incorrect; while transceivers have power meters, the specific term 'S meter' exclusively refers to the receiver's signal strength measurement. Carrier suppression and impedance require entirely different measurement tools, such as an oscilloscope or an antenna analyzer.