Question T0C03
From subelement T0 - T0C
How does the allowable power density for RF safety change if duty cycle changes from 100 percent to 50 percent?
Why is this correct?
When duty cycle drops from 100% to 50%, you're transmitting half the time, so average RF exposure is halved. The FCC compensates for this reduced exposure by allowing double the power density—increasing by a factor of 2. Think of it as a safety trade-off: less transmission time equals permission for higher instantaneous power while maintaining the same average exposure limits.
Memory tip
Remember the inverse relationship: when duty cycle goes down, allowable power density goes up proportionally. This pattern applies across all duty cycle calculations—50% duty cycle means 2x power allowance, 25% duty cycle means 4x power allowance, maintaining constant average exposure.
Learn more
This principle reflects how RF exposure regulations focus on average power density over time rather than instantaneous peaks. In practical amateur radio operation, modes like SSB naturally have lower duty cycles than FM because you're not transmitting during pauses in speech. CW has variable duty cycles depending on sending speed and spacing. Understanding duty cycle helps explain why some emission standards allow higher power levels—the regulatory framework accounts for the temporal nature of actual transmission patterns.
Think about it
Why do you think the FCC bases RF exposure limits on average power density over time periods rather than just instantaneous peak power levels?