*Question E9A11:
Which of the following determines ground losses for a ground-mounted vertical antenna operating on HF?*  

*Correct Answer is  C: Soil conductivity*  

### AI Response: (may contain errors)  

To determine ground losses for a ground-mounted vertical antenna operating on HF, the correct answer is:

**C: Soil conductivity**

### Explanation of the Correct Answer:
- **Soil Conductivity**: The conductivity of the soil directly affects how well the antenna can radiate energy into the ground and how much energy is lost as heat. Higher soil conductivity means lower ground losses, which results in better performance of the antenna. 

### Why the Other Choices are Incorrect:
- **A: The standing wave ratio (SWR)**: While SWR is important for ensuring efficient power transfer from the transmitter to the antenna, it does not directly determine ground losses. SWR indicates how well the antenna is matched to the transmission line, but it does not account for the characteristics of the ground beneath the antenna.

- **B: Distance from the transmitter**: The distance from the transmitter does not influence ground losses. Ground losses are primarily a function of the antenna's interaction with the ground, not the distance to the transmitter. 

- **D: Take-off angle**: The take-off angle refers to the angle at which the radio waves leave the antenna. While it can affect the coverage area and performance of the antenna, it does not determine ground losses. Ground losses are more about the soil properties than the radiation pattern.

### Useful Formulas or Rules of Thumb:
- Ground losses can be estimated using the following relationship:
  
$$
L_g = \frac{1}{\sigma}
$$

where:
- $L_g$ = ground loss in ohms
- $\sigma$ = soil conductivity in siemens per meter (S/m)

Higher conductivity ($\sigma$) results in lower ground losses ($L_g$), which is crucial for optimizing the performance of a ground-mounted vertical antenna. 

Understanding these concepts will help you grasp the factors affecting antenna performance and prepare effectively for the Extra Class exam.