Over what range of frequencies are the FCC human body RF exposure limits most restrictive?
The correct answer is C: 30 - 300 MHz. The FCC human body RF exposure limits are most restrictive over the range of 30 - 300 MHz. In this frequency range, the human body is most efficient at absorbing RF energy, so the limits are lowest (most restrictive).
The human body acts like an antenna, and it's most efficient (absorbs most RF energy) at frequencies around 30-300 MHz, which is near the body's resonant frequency. At these frequencies, RF energy is absorbed most effectively, creating the highest risk. Therefore, the MPE limits are most restrictive (lowest allowed exposure levels) in this range. At lower frequencies (below 30 MHz), the body is less efficient at absorbing RF. At higher frequencies (above 300 MHz), energy is absorbed more superficially. The 30-300 MHz range is where you need to be most careful about RF exposure.
Exam Tip
Most restrictive MPE = 30-300 MHz. Remember: FCC human body RF exposure limits are most restrictive over 30-300 MHz because the human body is most efficient at absorbing RF energy in this frequency range (near body resonance).
Memory Aid
"**M**ost **R**estrictive **M**PE = **3**0-**3**00 **M**Hz (think 'MRMPE = 30-300MHz')"
Real-World Application
You're evaluating RF exposure for your VHF station (146 MHz, in the 30-300 MHz range). The MPE limits are very strict here - maybe 0.2 mW/cm² for uncontrolled exposure. This is much stricter than at HF (below 30 MHz) where limits might be 0.6 mW/cm². The 30-300 MHz range requires extra care because the body absorbs RF most efficiently here.
FCC Part 97.13Key Concepts
Why Other Options Are Wrong
Option A: Incorrect. 300 kHz - 3 MHz is below the most restrictive range. The body is less efficient at absorbing RF at these lower frequencies.
Option B: Incorrect. 3 - 30 MHz is still below the most restrictive range, though getting closer. The most restrictive range starts at 30 MHz.
Option D: Incorrect. 300 - 3000 MHz is above the most restrictive range. At these higher frequencies, energy is absorbed more superficially, so limits are less restrictive.
题目解析
The correct answer is C: 30 - 300 MHz. The FCC human body RF exposure limits are most restrictive over the range of 30 - 300 MHz. In this frequency range, the human body is most efficient at absorbing RF energy, so the limits are lowest (most restrictive). The human body acts like an antenna, and it's most efficient (absorbs most RF energy) at frequencies around 30-300 MHz, which is near the body's resonant frequency. At these frequencies, RF energy is absorbed most effectively, creating the highest risk. Therefore, the MPE limits are most restrictive (lowest allowed exposure levels) in this range. At lower frequencies (below 30 MHz), the body is less efficient at absorbing RF. At higher frequencies (above 300 MHz), energy is absorbed more superficially. The 30-300 MHz range is where you need to be most careful about RF exposure.
考试技巧
Most restrictive MPE = 30-300 MHz. Remember: FCC human body RF exposure limits are most restrictive over 30-300 MHz because the human body is most efficient at absorbing RF energy in this frequency range (near body resonance).
记忆口诀
**M**ost **R**estrictive **M**PE = **3**0-**3**00 **M**Hz (think 'MRMPE = 30-300MHz')
实际应用示例
You're evaluating RF exposure for your VHF station (146 MHz, in the 30-300 MHz range). The MPE limits are very strict here - maybe 0.2 mW/cm² for uncontrolled exposure. This is much stricter than at HF (below 30 MHz) where limits might be 0.6 mW/cm². The 30-300 MHz range requires extra care because the body absorbs RF most efficiently here.
错误选项分析
Option A: Incorrect. 300 kHz - 3 MHz is below the most restrictive range. The body is less efficient at absorbing RF at these lower frequencies. Option B: Incorrect. 3 - 30 MHz is still below the most restrictive range, though getting closer. The most restrictive range starts at 30 MHz. Option D: Incorrect. 300 - 3000 MHz is above the most restrictive range. At these higher frequencies, energy is absorbed more superficially, so limits are less restrictive.
知识点
RF exposure limits, 30-300 MHz, Most restrictive, Body resonance
Verified Content
Question from official FCC Extra Class question pool. Explanation reviewed by licensed amateur radio operators.