*Question G4B11:
Which of the following must be connected to an antenna analyzer when it is being used for SWR measurements?*  

*Correct Answer is  C: Antenna and feed line*  

### AI Response: (may contain errors)  

To measure the Standing Wave Ratio (SWR) using an antenna analyzer, you need to connect the analyzer directly to the antenna system, which includes the antenna and the feed line. This setup allows the analyzer to measure the impedance and SWR of the antenna system accurately.

### Explanation:

1. **Correct Answer: Antenna and feed line**
   - The antenna analyzer is designed to measure the characteristics of the antenna system, including SWR, impedance, and resonance. By connecting it to the antenna and feed line, you can determine how well the antenna is matched to the transmission line, which is crucial for efficient power transfer.

2. **Why the other choices are incorrect:**
   - **Receiver:** A receiver is not involved in measuring SWR. SWR measurements are concerned with the transmission path, not the reception path.
   - **Transmitter:** While a transmitter can be used to generate a signal for SWR measurement, it is not necessary when using an antenna analyzer. The analyzer itself generates the necessary test signals.
   - **All these choices are correct:** This option is incorrect because neither the receiver nor the transmitter needs to be connected for SWR measurements with an antenna analyzer.

### Useful Concepts:

- **SWR (Standing Wave Ratio):** A measure of how well the antenna system is matched to the transmission line. An SWR of 1:1 indicates a perfect match, while higher values indicate mismatches.
- **Impedance Matching:** Ensuring that the antenna's impedance is as close as possible to the transmission line's characteristic impedance (usually 50 ohms) to minimize reflections and maximize power transfer.

By connecting the antenna analyzer to the antenna and feed line, you can effectively measure and adjust the system for optimal performance.