Question T0C10
From subelement T0 - T0C
Why is duty cycle one of the factors used to determine safe RF radiation exposure levels?
Why is this correct?
Duty cycle is the percentage of time a transmitter is actually transmitting. Since RF exposure limits are based on average exposure over time, not peak exposure, duty cycle directly affects the average radiation exposure. If you transmit 50% of the time instead of 100%, your average RF output is cut in half, reducing exposure proportionally. Peak exposure (B) isn't the concern—it's the time-averaged exposure that matters for safety calculations.
Memory tip
Think 'average over time' whenever you see duty cycle in RF safety questions. The FCC cares about cumulative exposure effects, not instantaneous peaks. Lower duty cycle allows higher power levels while maintaining the same average exposure—it's a trade-off between power and transmission time.
Learn more
RF exposure regulations focus on thermal heating effects in human tissue, which depend on average power absorbed over time rather than instantaneous power levels. This is why continuous wave modes like FM have 100% duty cycle and require lower power levels for compliance, while modes like SSB voice (around 20% duty cycle) or digital modes can often use higher peak power while maintaining equivalent average exposure levels under Part 97 emission standards.
Think about it
Why do you think the FCC bases exposure limits on average power over time rather than peak power, and how might this affect your choice of operating modes at different power levels?