*Question G0A07:
What is the effect of modulation duty cycle on RF exposure?*  

*Correct Answer is  A: A lower duty cycle permits greater power levels to be transmitted*  

### AI Response: (may contain errors)  

The correct answer to the question about the effect of modulation duty cycle on RF exposure is:

**A: A lower duty cycle permits greater power levels to be transmitted.**

### Explanation of the Correct Answer:
- **Duty Cycle** refers to the fraction of time a transmitter is actively transmitting compared to the total time it is on. It is usually expressed as a percentage.
- A **lower duty cycle** means that the transmitter is on for a shorter period of time relative to the total time. This results in a lower average power output over time, which can allow for higher peak power levels without exceeding RF exposure limits.
- Since RF exposure limits are based on average power over time, a lower duty cycle allows for higher instantaneous power levels while still complying with safety regulations.

### Why the Other Choices are Incorrect:
- **B: A higher duty cycle permits greater power levels to be transmitted.**
  - This is incorrect because a higher duty cycle means the transmitter is on for a longer period, leading to a higher average power output. This can exceed RF exposure limits, making it unsafe to transmit at high power levels continuously.

- **C: Low duty cycle transmitters are exempt from RF exposure evaluation requirements.**
  - This is incorrect because all transmitters, regardless of duty cycle, must comply with RF exposure evaluation requirements. The duty cycle may influence the power levels that can be safely transmitted, but it does not exempt a transmitter from evaluation.

- **D: High duty cycle transmitters are exempt from RF exposure requirements.**
  - This is also incorrect. High duty cycle transmitters are subject to stricter RF exposure evaluations because they operate at higher average power levels, which can pose a greater risk of exposure.

### Useful Rules of Thumb:
- **Average Power Calculation**: The average power ($P_{avg}$) can be calculated using the formula:
  
  $$P_{avg} = P_{peak} \times Duty \ Cycle$$

  where:
  - $P_{peak}$ = peak power output
  - $Duty \ Cycle$ = duty cycle (expressed as a decimal)

- **Safety Compliance**: Always ensure that the average power output does not exceed the limits set by the FCC or other regulatory bodies, regardless of the duty cycle. 

Understanding these concepts will help you grasp the relationship between duty cycle and RF exposure, which is crucial for the Extra Class exam.