Which of the following instruments can be used to determine if an antenna is resonant at the desired operating frequency?

An antenna analyzer is specifically designed to measure the impedance of an antenna at various frequencies, making it a valuable tool for determining whether an antenna is resonant at a desired operating frequency. When an antenna is resonant, its impedance will match the characteristics of the transmission line and the radio, typically making the SWR (Standing Wave Ratio) low. An antenna analyzer provides real-time readings of SWR, impedance, and other electrical parameters, allowing the operator to determine if the antenna is tuned correctly for their intended frequency of transmission.

In contrast, while other instruments like a VTVM (Vacuum Tube Volt Meter) can measure voltage and can be helpful in certain applications, they do not provide specific information about antenna resonance. A "Q" meter measures the quality factor of coils and resonant circuits but is not tailored for antenna resonance evaluation. A frequency counter also measures the frequency of signals but does not give insight into the antenna's tuning or impedance characteristics. Therefore, the antenna analyzer is the most appropriate choice for assessing the resonance of an antenna at a specific operating frequency.