*Question G0A12:
[1.1307(1)(b)(3)(i)(A)] What stations are subject to the FCC rules on RF exposure?*  

*Correct Answer is  D: All stations with a time-averaged transmission of more than one milliwatt*  

### AI Response: (may contain errors)  

The correct answer is D: All stations with a time-averaged transmission of more than one milliwatt.

1. **Why the correct answer is correct:**
   - The FCC rules on RF exposure apply to all radio stations, including amateur radio stations, that have a time-averaged power output exceeding one milliwatt. This is to ensure that all stations, regardless of their type, adhere to safety standards to protect humans from excessive radio frequency exposure.

2. **Why the other choices are incorrect:**
   - **Choice A:** "All commercial stations; amateur radio stations are exempt" is incorrect because amateur radio stations are not exempt from RF exposure rules. All stations, including amateur ones, must comply if they exceed the specified power threshold.
   - **Choice B:** "Only stations with antennas lower than one wavelength above the ground" is incorrect because the height of the antenna is not a determining factor for RF exposure compliance. The rule is based on power output, not antenna height.
   - **Choice C:** "Only stations transmitting more than 500 watts PEP" is incorrect because the threshold for RF exposure rules is much lower than 500 watts. It is based on a time-averaged power of more than one milliwatt, not peak envelope power (PEP).

3. **Useful rules of thumb:**
   - The key factor for RF exposure compliance is the time-averaged power output. If a station's average power exceeds one milliwatt, it must adhere to RF exposure guidelines.
   - Time-averaged power considers both the power level and the duty cycle of the transmission, ensuring that even low-power stations are evaluated for potential RF exposure risks.