What is the definition of duty cycle during the averaging time for RF exposure?

In the context of RF exposure evaluations, "duty cycle" refers specifically to the percentage of time that a transmitter is actively producing RF energy during a given averaging period. If a transmitter is keyed down for 3 minutes and unkeyed for 3 minutes during a 6-minute window, its duty cycle is 50 percent. This concept is crucial for calculating average RF exposure. Biological heating effects from RF energy depend on the average power absorbed over time. A 100-watt transmitter operating at a 50 percent duty cycle will produce the same average RF exposure as a 50-watt transmitter running continuously (100 percent duty cycle). Different operating modes naturally have different duty cycles. For example, SSB voice and CW only transmit power during active speech or key down, resulting in a lower duty cycle than modes like FM or FT8, which transmit a continuous carrier at full power.