How does the allowable power density for RF safety change if duty cycle changes from 100 percent to 50 percent?
The correct answer is C: It increases by a factor of 2. If duty cycle changes from 100 percent to 50 percent, the allowable power density for RF safety increases by a factor of 2. Duty cycle is the percentage of time transmitting. Lower duty cycle means less average exposure, so you can use higher power density. If duty cycle halves (100% to 50%), allowable power density doubles. For amateur radio operators, this means SSB (lower duty cycle) allows higher power than CW or FM (higher duty cycle) for the same exposure limit. Understanding this helps optimize power while staying within limits.
Exam Tip
Duty cycle 100% to 50% = power density doubles. Think 'D'uty cycle 'H'alves = 'D'ensity 'D'oubles. Lower duty cycle (less transmitting time) allows higher power density. Inverse relationship - half the duty cycle, double the power.
Memory Aid
"Duty cycle 100% to 50% = power density doubles. Think 'D'uty cycle 'H'alves = 'D'ensity 'D'oubles. Lower duty cycle allows higher power for same exposure. Inverse relationship."
Real-World Application
You operate CW with 100% duty cycle (continuous transmission) at 100 watts, which is at the exposure limit. You switch to SSB with 50% duty cycle (talking half the time). Now you can operate at 200 watts and still meet the same exposure limit because your average exposure is the same (200W × 50% = 100W average, same as 100W × 100%).
Key Concepts
Why Other Options Are Wrong
Option A: Incorrect. It doesn't increase by a factor of 3 - if duty cycle halves, power density doubles (factor of 2), not triples.
Option B: Incorrect. It doesn't decrease by 50% - lower duty cycle allows higher power density, not lower. The relationship is inverse.
Option D: Incorrect. Lower duty cycle does allow adjustment - it's a valid way to increase allowable power density. The adjustment is a factor of 2.
题目解析
The correct answer is C: It increases by a factor of 2. If duty cycle changes from 100 percent to 50 percent, the allowable power density for RF safety increases by a factor of 2. Duty cycle is the percentage of time transmitting. Lower duty cycle means less average exposure, so you can use higher power density. If duty cycle halves (100% to 50%), allowable power density doubles. For amateur radio operators, this means SSB (lower duty cycle) allows higher power than CW or FM (higher duty cycle) for the same exposure limit. Understanding this helps optimize power while staying within limits.
考试技巧
Duty cycle 100% to 50% = power density doubles. Think 'D'uty cycle 'H'alves = 'D'ensity 'D'oubles. Lower duty cycle (less transmitting time) allows higher power density. Inverse relationship - half the duty cycle, double the power.
记忆口诀
Duty cycle 100% to 50% = power density doubles. Think 'D'uty cycle 'H'alves = 'D'ensity 'D'oubles. Lower duty cycle allows higher power for same exposure. Inverse relationship.
实际应用示例
You operate CW with 100% duty cycle (continuous transmission) at 100 watts, which is at the exposure limit. You switch to SSB with 50% duty cycle (talking half the time). Now you can operate at 200 watts and still meet the same exposure limit because your average exposure is the same (200W × 50% = 100W average, same as 100W × 100%).
错误选项分析
Option A: Incorrect. It doesn't increase by a factor of 3 - if duty cycle halves, power density doubles (factor of 2), not triples. Option B: Incorrect. It doesn't decrease by 50% - lower duty cycle allows higher power density, not lower. The relationship is inverse. Option D: Incorrect. Lower duty cycle does allow adjustment - it's a valid way to increase allowable power density. The adjustment is a factor of 2.
知识点
Duty cycle, RF exposure limits, Power density, RF safety
Verified Content
Question from official FCC Technician Class question pool. Explanation reviewed by licensed amateur radio operators.