*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 that can measure various parameters related to antennas and transmission lines. Let's explore why each choice is correct:

1. **Velocity Factor**:  
   - The velocity factor of a transmission line is the ratio of the speed of a signal in the cable to the speed of light in a vacuum. An antenna analyzer can measure the velocity factor by analyzing the phase shift of a signal as it travels through the cable. This is useful for determining the electrical length of the cable.

2. **Cable Length**:  
   - By using the velocity factor and measuring the time delay or phase shift of a signal, an antenna analyzer can calculate the physical length of a cable. This is done by sending a signal down the cable and measuring the time it takes to return.

3. **Resonant Frequency of a Tuned Circuit**:  
   - An antenna analyzer can measure the resonant frequency of a tuned circuit by sweeping through a range of frequencies and identifying the frequency at which the circuit exhibits minimum impedance or maximum reactance cancellation.

Since an antenna analyzer can perform all these measurements, the correct answer is:

- **D: All these choices are correct**

### Why the Other Choices Are Incorrect Individually:
- **A: Velocity factor**: While correct, it is not the only parameter that can be measured.
- **B: Cable length**: Also correct, but not the only parameter measurable.
- **C: Resonant frequency of a tuned circuit**: Correct, but again, not the only parameter.

### Useful Formulas:
- **Velocity Factor ($VF$)**:  
  $$ VF = \frac{\text{Speed of signal in cable}}{\text{Speed of light in vacuum}} $$

- **Cable Length ($L$)**:  
  $$ L = \frac{c \times \text{Time delay}}{2 \times VF} $$  
  where $c$ is the speed of light.

An antenna analyzer's ability to measure these parameters makes it a powerful tool for amateur radio operators.