Question E0A02:
When evaluating RF exposure levels from your station at a neighbor’s home, what must you do?  

Choices:  
A: Ensure signals from your station are less than the controlled maximum permissible exposure (MPE) limits  
B: Ensure signals from your station are less than the uncontrolled maximum permissible exposure (MPE) limits  
C: Ensure signals from your station are less than the controlled maximum permissible emission (MPE) limits  
D: Ensure signals from your station are less than the uncontrolled maximum permissible emission (MPE) limits    

Correct Answer is  B: Ensure signals from your station are less than the uncontrolled maximum permissible exposure (MPE) limits  

To evaluate RF exposure at a neighbor’s home, you must use the “uncontrolled” (general population) limits, because neighbors are not trained/aware participants who can control their exposure.

Why B is correct
- A neighbor’s home is an uncontrolled environment (general population).
- FCC rules require your station’s fields at that location to be below the uncontrolled Maximum Permissible Exposure (MPE) limits for the operating frequency.

Why the others are incorrect
- A: “Controlled” MPE applies only to occupationally/aware persons who can take steps to limit exposure (e.g., you or trained helpers on your property). Neighbors do not qualify.
- C and D: MPE means Maximum Permissible Exposure, not “emission.” The FCC limits are exposure limits, not emission limits.

Useful formulas and rules of thumb
- Far-field power density:
  $$S = \frac{P_T G}{4\pi r^2} \quad \text{(W/m}^2\text{)}$$
  where $P_T$ is transmitter power (W), $G$ is antenna gain (linear), and $r$ is distance (m).
- Field relationships:
  $$S = \frac{E^2}{377} = 377\,H^2$$
  so
  $$E = \sqrt{377\,S}, \quad H = \sqrt{\frac{S}{377}}$$
- Safe distance for a given MPE limit $S_{\text{MPE}}$:
  $$r_{\min} = \sqrt{\frac{P_T G}{4\pi S_{\text{MPE}}}}$$
- Time averaging:
  - Uncontrolled/general population: average over 30 minutes.
  - Controlled/occupational: average over 6 minutes.
  - Include duty factor and transmit-time fraction, e.g.,
    $$P_{\text{avg}} = P_{\text{peak}} \times \text{duty cycle} \times \text{transmit fraction}$$
- Rule of thumb:
  - Uncontrolled limits are lower (more restrictive) than controlled limits.
  - Exposure falls with the inverse square of distance; doubling distance reduces $S$ by a factor of 4.

For the exam: At a neighbor’s home, compare your calculated or measured fields to the uncontrolled MPE limits for your frequency and ensure they are below those limits.