*Question E4A11:
Which of the following can be measured with an antenna analyzer?*  

*Correct Answer is  D: All these choices are correct*  

### AI Response: (may contain errors)  

An antenna analyzer is a versatile tool used in amateur radio to assess various parameters of antennas and transmission lines. Let's break down the question and the answer choices.

### Correct Answer: D - All these choices are correct

1. **Why the correct answer is correct:**
   - An antenna analyzer can measure:
     - **Velocity factor**: This is the ratio of the speed of a signal in a transmission line to the speed of light in a vacuum. It helps in determining how fast signals travel through the cable.
     - **Cable length**: By measuring the time it takes for a signal to travel down the cable and back, the analyzer can calculate the length of the cable.
     - **Resonant frequency of a tuned circuit**: The analyzer can determine the frequency at which an antenna or circuit resonates, which is crucial for tuning and optimizing performance.

### Why the other choices are incorrect:
- **A: Velocity factor**: This choice is actually correct, as the analyzer can measure it.
- **B: Cable length**: This choice is also correct, as the analyzer can measure it.
- **C: Resonant frequency of a tuned circuit**: This choice is correct as well, since the analyzer can measure resonant frequency.

### Summary:
Since all the individual choices (A, B, and C) are correct, the answer D ("All these choices are correct") is the best choice. 

### Useful Concepts:
- **Velocity Factor (VF)**: It is calculated as:
  $$ VF = \frac{v}{c} $$
  where:
  - $v$ = speed of the signal in the cable
  - $c$ = speed of light in a vacuum (approximately $3 \times 10^8$ m/s)

- **Cable Length Measurement**: The time delay of the signal can be used to find the length:
  $$ L = \frac{t \times v}{2} $$
  where:
  - $L$ = length of the cable
  - $t$ = time taken for the signal to travel to the end of the cable and back
  - $v$ = speed of the signal in the cable

Understanding these concepts will help you effectively use an antenna analyzer and prepare for the Extra Class exam.