*Question G4B13:
Which of the following can be measured with an antenna analyzer?*  

*Correct Answer is  C: Impedance of coaxial cable*  

### AI Response: (may contain errors)  

An antenna analyzer is a specialized tool used to assess various parameters of antennas and their feedlines. Let's break down the question regarding what can be measured with an antenna analyzer.

### Correct Answer: C - Impedance of coaxial cable

- **Why it's correct**: An antenna analyzer can measure the impedance of an antenna system, which includes the coaxial cable. The impedance is crucial for ensuring that the antenna is matched to the transmission line, minimizing reflections and maximizing power transfer. The analyzer provides readings of the impedance at different frequencies, helping to identify any mismatches.

### Why the other choices are incorrect:

- **A: Front-to-back ratio of an antenna**  
  - **Explanation**: The front-to-back ratio is a measure of how well an antenna can reject signals from the rear compared to the front. This is typically measured using a directional antenna and a signal source, not with an antenna analyzer.

- **B: Power output from a transmitter**  
  - **Explanation**: An antenna analyzer does not measure power output directly. Power output is typically measured with a wattmeter, which can provide readings of the actual power being transmitted.

- **D: Gain of a directional antenna**  
  - **Explanation**: While an antenna analyzer can provide some information about the impedance and SWR (Standing Wave Ratio), it does not measure the gain of an antenna. Gain is usually determined through field strength measurements or by comparing the antenna's performance to a reference antenna.

### Useful Formulas and Rules of Thumb:

- **Impedance Matching**:  
  To ensure maximum power transfer, the impedance of the antenna should match the impedance of the transmission line (usually 50 ohms for most amateur radio applications). The formula for impedance matching is:

  $$ Z_L = Z_0 $$

  where:
  - $Z_L$ = load impedance (antenna)
  - $Z_0$ = characteristic impedance of the transmission line

- **SWR Calculation**:  
  The Standing Wave Ratio (SWR) can be calculated using the formula:

  $$ SWR = \frac{1 + \Gamma}{1 - \Gamma} $$

  where $\Gamma$ (the reflection coefficient) can be derived from the impedance measurements.

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