*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 understand why the correct answer is "Antenna and feed line," let's break down the question and the choices:

1. **Correct Answer: Antenna and feed line (Choice C)**
   - An antenna analyzer is specifically designed to measure the standing wave ratio (SWR) of an antenna system. For accurate SWR measurements, the analyzer must be connected to the antenna and the feed line. This setup allows the analyzer to assess how well the antenna is radiating the RF energy transmitted through the feed line. If the antenna and feed line are not connected, the analyzer cannot provide meaningful SWR readings.

2. **Why the other choices are incorrect:**
   - **A: Receiver**
     - A receiver is not necessary for SWR measurements. The purpose of measuring SWR is to evaluate the efficiency of the antenna system, not to receive signals. Therefore, connecting a receiver does not contribute to the SWR measurement process.
   - **B: Transmitter**
     - While a transmitter is involved in the overall operation of an antenna system, it is not required for SWR measurements with an analyzer. The analyzer can measure SWR without a transmitter, as it can generate its own test signals. Connecting a transmitter could potentially lead to damage if the analyzer is not designed to handle high power levels.
   - **D: All these choices are correct**
     - This choice is incorrect because, as explained, neither the receiver nor the transmitter is necessary for SWR measurements. Only the antenna and feed line are required.

3. **Useful formulas or rules of thumb:**
   - The SWR can be calculated using the formula:
   $$ 
   SWR = \frac{V_{max}}{V_{min}} 
   $$
   where:
   - $V_{max}$ = maximum voltage along the feed line
   - $V_{min}$ = minimum voltage along the feed line

   - A common rule of thumb is that an SWR of 1:1 is ideal, indicating perfect matching between the antenna and feed line, while an SWR of 2:1 is generally acceptable for most applications.

In summary, for SWR measurements, the antenna and feed line must be connected to the analyzer to obtain accurate readings, while the receiver and transmitter are not needed for this specific measurement.