*Question G4B10:
Which of the following can be determined with a directional wattmeter?*  

*Correct Answer is  A: Standing wave ratio*  

### AI Response: (may contain errors)  

A directional wattmeter is a device used to measure the power flowing in a transmission line, both forward and reflected. This makes it particularly useful for determining the Standing Wave Ratio (SWR).

### Explanation:

1. **Correct Answer: Standing wave ratio (SWR)**
   - **Why it's correct:**  
     A directional wattmeter can measure both the forward power and the reflected power in a transmission line. The SWR is a measure of how well the antenna system is matched to the transmission line and is calculated using these power measurements. The formula for SWR is:
     $$ \text{SWR} = \frac{1 + \sqrt{\frac{P_{\text{reflected}}}{P_{\text{forward}}}}}{1 - \sqrt{\frac{P_{\text{reflected}}}{P_{\text{forward}}}}} $$
     where:
     - $P_{\text{forward}}$ is the forward power
     - $P_{\text{reflected}}$ is the reflected power

2. **Why the other choices are incorrect:**
   - **Antenna front-to-back ratio:**  
     This is a measure of an antenna's ability to reject signals from the back compared to the front. It requires pattern measurements, not power measurements, and thus cannot be determined with a directional wattmeter.
   
   - **RF interference:**  
     RF interference involves unwanted signals affecting the desired communication and is typically analyzed using spectrum analyzers or other diagnostic tools, not a directional wattmeter.
   
   - **Radio wave propagation:**  
     This refers to how radio waves travel through the environment, which involves factors like frequency, terrain, and atmospheric conditions. A directional wattmeter does not provide information on propagation characteristics.

In summary, a directional wattmeter is specifically suited for measuring SWR by using forward and reflected power, making it the correct tool for this purpose.