Why is duty cycle one of the factors used to determine safe RF radiation exposure levels?

Duty cycle is an important factor in determining safe RF radiation exposure levels because it fundamentally influences the average amount of radiation an individual is exposed to over time. The duty cycle refers to the fraction of time that a system is actively transmitting compared to the total time it is in operation.

When considering RF radiation, if a transmitter operates at a duty cycle that is less than 100%, it means that it is only transmitting for part of the time, resulting in lower average exposure levels. As such, even if the peak power output during transmission is high, the average power (and thus the average radiation exposure) over time is reduced. Regulatory standards often focus on average exposure due to its relevance in assessing health risks.

In contrast, peak exposure considers only the highest levels of output without accounting for how often that peak is maintained. This could lead to misunderstandings about the actual exposure risks. Options that reference feed line loss or thermal effects of the final amplifier focus on different technical aspects of RF transmission and are not directly related to the concept of exposure over time, which is crucial for safety assessments. Hence, the understanding of average radiation exposure length, moderated by duty cycle, plays a significant role in establishing safe practices for RF use.