ARRL Technician Practice Exam

Which frequency has the lowest value for Maximum Permissible Exposure limits?

1. 30 MHz

2. 50 MHz

3. 100 MHz

4. 150 MHz

The correct answer is: 50 MHz

The correct answer indicates that the frequency of 50 MHz has the lowest Maximum Permissible Exposure (MPE) limits when compared to the other provided frequencies. This is due to how radiofrequency (RF) exposure limits are generally established based on frequency; specifically, the interaction of RF energy with biological tissue varies across different frequencies. At lower frequencies, specifically below 100 MHz, the limits for MPE tend to be lower because tissue absorbs energy differently than at higher frequencies. As frequencies increase, the body could potentially absorb more energy resulting in higher permissible exposure limits. Consequently, the MPE limits are designed to minimize potential health risks associated with prolonged exposure to RF energy. In contrast, frequencies of 30 MHz, 100 MHz, and 150 MHz have higher MPE limits because as frequency increases, the biological effects of RF exposure are generally less pronounced for similar exposure durations. Therefore, the lower MPE limit at 50 MHz reflects a more conservative approach to ensure safety at this particular range, emphasizing the importance of regulating exposure in the context of RF energy safety standards.