Question
What is the effect of modulation duty cycle on RF exposure?
Answer Options
- A) A lower duty cycle permits greater power levels to be transmitted
- B) A higher duty cycle permits greater power levels to be transmitted
- C) Low duty cycle transmitters are exempt from RF exposure evaluation requirements
- D) High duty cycle transmitters are exempt from RF exposure requirements
Correct Answer: A
Explanation
The duty cycle of a modulation mode (the fraction of time the transmitter is at peak power) is critical for determining the time-averaged RF exposure. Since the MPE limits are based on the average power over a given time, a mode that transmits continuously heats tissue more than a pulsed or intermittent mode at the same peak power.
Therefore, a lower duty cycle permits greater power levels to be transmitted while keeping the time-averaged power below the MPE limit. For example, a 1500 W PEP SSB signal (\approx 20\% duty cycle) might be MPE compliant, whereas a 1500 W FM signal (\approx 100\% duty cycle) would require a significant reduction in power to be MPE compliant.
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