Explanation: A spectrum analyzer is the correct instrument because it graphically displays the amplitude of signals as a function of frequency. This allows an operator to visualize the desired transmission frequency along with any unwanted emissions, such as harmonics, parasitics, or other spurious signals, that might be present in the transmitter's output. FCC regulations are strict about limiting these unwanted emissions. A wattmeter measures the total power output but does not show individual frequency components. A logic analyzer is used for examining digital circuits and signals, not radio frequency outputs. A time domain reflectometer (TDR) is used to locate faults or impedance mismatches in transmission lines, not to analyze the spectral content of a transmitter's output.