*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 versatile tool primarily used for measuring the impedance characteristics of antennas and transmission lines. Let's break down the options:

1. **Correct Answer: Impedance of coaxial cable (C)**  
   - An antenna analyzer can measure the impedance of coaxial cables. Impedance is a complex quantity that includes both resistance and reactance, and it is crucial for ensuring that the transmission line is properly matched to the antenna system. The analyzer provides readings of impedance at various frequencies, helping to identify mismatches or faults in the cable.

2. **Why the other choices are incorrect:**

   - **Front-to-back ratio of an antenna (A):**  
     - The front-to-back ratio is a measure of an antenna's directivity, specifically the ratio of power radiated in the forward direction to that in the backward direction. This requires measuring the radiation pattern, which is not something an antenna analyzer can do. Instead, this is typically measured in an antenna test range or using specialized equipment.

   - **Power output from a transmitter (B):**  
     - An antenna analyzer is not designed to measure power output. Power output is typically measured with a power meter, which can handle the high power levels from a transmitter and provide accurate readings.

   - **Gain of a directional antenna (D):**  
     - Antenna gain is a measure of how well an antenna directs radio frequency energy in a particular direction compared to a reference antenna. Measuring gain requires comparing the antenna's performance to a known standard, often in a controlled environment, which is beyond the capabilities of an antenna analyzer.

In summary, an antenna analyzer is best suited for measuring impedance-related parameters, making option C the correct choice.