ARRL Technician Practice Exam

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

1. A frequency counter

2. An oscilloscope

3. An antenna analyzer

4. A signal generator

The correct answer is: An antenna analyzer

An antenna analyzer is specifically designed to provide information about the impedance of an antenna system at various frequencies, which helps in assessing if the antenna is resonant at the desired operating frequency. It measures parameters such as standing wave ratio (SWR), impedance, and resonance, making it an effective tool for fine-tuning antennas. When an antenna is resonant, it typically has a specific impedance (often 50 ohms in many cases) at the desired operating frequency, leading to minimal reflected power and optimal performance. The antenna analyzer allows users to easily identify the frequency at which the antenna shows the best match, thereby confirming resonance. The other instruments listed serve different purposes. A frequency counter measures the frequency of incoming signals but does not provide information on the antenna's resonance characteristics. An oscilloscope primarily visualizes waveforms and does not directly measure antenna resonance or impedance. A signal generator produces signals at specific frequencies but does not measure how well the antenna can receive or transmit those frequencies. Therefore, while all the mentioned tools have their uses in radio and electronics, the antenna analyzer is uniquely suited for determining antenna resonance.