*Question T7C02:
Which of the following is used to determine if an antenna is resonant at the desired operating frequency?*  

*Correct Answer is  B: An antenna analyzer*  

### AI Response: (may contain errors)  

To determine if an antenna is resonant at the desired operating frequency, the correct tool to use is an **antenna analyzer**.

### Explanation of the Correct Answer:
- **B: An antenna analyzer**: 
  - This device measures the impedance of the antenna at various frequencies. It can show the standing wave ratio (SWR) and help identify the frequency at which the antenna is resonant. A resonant antenna will have a low SWR at its operating frequency, indicating efficient power transfer.

### Explanation of Incorrect Answers:
- **A: A VTVM (Vacuum Tube Volt Meter)**: 
  - A VTVM is primarily used for measuring voltage levels in circuits. It does not provide information about antenna impedance or resonance.

- **C: A Q meter**: 
  - A Q meter measures the quality factor (Q) of resonant circuits, which relates to bandwidth and energy loss. While it can provide some information about resonant circuits, it is not specifically designed to analyze antennas for resonance at a particular frequency.

- **D: A frequency counter**: 
  - A frequency counter measures the frequency of a signal but does not provide information about the antenna's impedance or whether it is resonant at that frequency.

### Summary:
- The **antenna analyzer** is the best tool for determining antenna resonance because it directly measures impedance and SWR, which are critical for assessing resonance.
- Other tools like VTVMs, Q meters, and frequency counters serve different purposes and do not provide the necessary information for antenna resonance analysis. 

### Useful Rule of Thumb:
- A good rule of thumb is that an antenna is considered resonant when its feedpoint impedance is close to 50 ohms (for most HF antennas) and the SWR is less than 2:1 at the desired operating frequency.