What parameter evaluates distortion of an AFSK signal caused by excessive input audio levels?
The correct answer is D: Intermodulation Distortion (IMD). The parameter that evaluates distortion of an AFSK signal caused by excessive input audio levels is Intermodulation Distortion (IMD). IMD measures unwanted frequency components created by nonlinear distortion.
When an AFSK signal is overmodulated due to excessive audio levels, the transmitter operates in a nonlinear region, creating intermodulation products. IMD measures these unwanted frequency components (harmonics and sum/difference frequencies) that appear due to the distortion. High IMD indicates poor signal quality and interference to adjacent frequencies. IMD is measured as the ratio of distortion products to the desired signal, typically expressed in decibels. Lower IMD is better - it indicates less distortion and a cleaner signal.
Exam Tip
AFSK distortion parameter = IMD. Remember: Intermodulation Distortion (IMD) evaluates distortion of AFSK signals caused by excessive input audio levels. IMD measures unwanted frequency components from nonlinear distortion.
Memory Aid
"**A**FSK **D**istortion = **I**ntermodulation **D**istortion (think 'AD = ID' = IMD)"
Real-World Application
You're testing your AFSK signal and find high IMD levels. This indicates your audio input is too high, causing overmodulation and distortion. You reduce the audio level, and the IMD decreases. Lower IMD means a cleaner signal with less interference to adjacent frequencies. IMD is a key parameter for evaluating AFSK signal quality.
FCC Part 97.307Key Concepts
Why Other Options Are Wrong
Option A: Incorrect. Signal-to-noise ratio measures noise, not distortion. IMD specifically measures distortion products, not noise.
Option B: Incorrect. Baud error rate measures data errors, not signal distortion. It's about bit errors, not signal quality.
Option C: Incorrect. Repeat Request Rate (RRR) measures how often retransmissions are needed, not signal distortion. It's a protocol metric, not a signal quality measurement.
题目解析
The correct answer is D: Intermodulation Distortion (IMD). The parameter that evaluates distortion of an AFSK signal caused by excessive input audio levels is Intermodulation Distortion (IMD). IMD measures unwanted frequency components created by nonlinear distortion. When an AFSK signal is overmodulated due to excessive audio levels, the transmitter operates in a nonlinear region, creating intermodulation products. IMD measures these unwanted frequency components (harmonics and sum/difference frequencies) that appear due to the distortion. High IMD indicates poor signal quality and interference to adjacent frequencies. IMD is measured as the ratio of distortion products to the desired signal, typically expressed in decibels. Lower IMD is better - it indicates less distortion and a cleaner signal.
考试技巧
AFSK distortion parameter = IMD. Remember: Intermodulation Distortion (IMD) evaluates distortion of AFSK signals caused by excessive input audio levels. IMD measures unwanted frequency components from nonlinear distortion.
记忆口诀
**A**FSK **D**istortion = **I**ntermodulation **D**istortion (think 'AD = ID' = IMD)
实际应用示例
You're testing your AFSK signal and find high IMD levels. This indicates your audio input is too high, causing overmodulation and distortion. You reduce the audio level, and the IMD decreases. Lower IMD means a cleaner signal with less interference to adjacent frequencies. IMD is a key parameter for evaluating AFSK signal quality.
错误选项分析
Option A: Incorrect. Signal-to-noise ratio measures noise, not distortion. IMD specifically measures distortion products, not noise. Option B: Incorrect. Baud error rate measures data errors, not signal distortion. It's about bit errors, not signal quality. Option C: Incorrect. Repeat Request Rate (RRR) measures how often retransmissions are needed, not signal distortion. It's a protocol metric, not a signal quality measurement.
知识点
Intermodulation distortion, IMD, AFSK, Distortion measurement
Verified Content
Question from official FCC Extra Class question pool. Explanation reviewed by licensed amateur radio operators.