What is considered an acceptable maximum IMD level for an idling PSK signal?
The correct answer is D: -30 dB. An acceptable maximum IMD level for an idling PSK signal is -30 dB or lower. This means the intermodulation distortion products should be at least 30 dB below the desired signal.
For PSK signals, especially when idling (not actively transmitting data), IMD should be very low to avoid interference. -30 dB IMD means the distortion products are 30 dB below the signal level, which is acceptable for clean operation. Higher IMD levels (like +5 dB, +10 dB, or +15 dB) would be terrible - they would mean distortion products are stronger than or equal to the signal, which is completely unacceptable. For good signal quality, IMD should be well below the signal level (negative dB values).
Exam Tip
PSK IMD maximum = -30 dB. Remember: Acceptable maximum IMD for an idling PSK signal is -30 dB (distortion 30 dB below signal). Positive IMD values are unacceptable.
Memory Aid
"**P**SK **I**MD **M**ax = **-3**0 **d**B (think 'PIM = -30dB')"
Real-World Application
You're testing your PSK signal and measure -35 dB IMD. This is good - the distortion products are 35 dB below your signal level, which is better than the -30 dB maximum. If you measured +5 dB IMD, that would be terrible - distortion stronger than your signal. For clean PSK operation, IMD should be -30 dB or lower.
FCC Part 97.307Key Concepts
Why Other Options Are Wrong
Option A: Incorrect. +5 dB IMD would mean distortion products are 5 dB stronger than the signal, which is terrible and completely unacceptable. IMD should be negative (below the signal).
Option B: Incorrect. +10 dB IMD would mean distortion is 10 dB stronger than the signal, which is even worse. This is completely unacceptable.
Option C: Incorrect. +15 dB IMD would mean distortion is 15 dB stronger than the signal, which is extremely bad. IMD must be negative (below signal level).
题目解析
The correct answer is D: -30 dB. An acceptable maximum IMD level for an idling PSK signal is -30 dB or lower. This means the intermodulation distortion products should be at least 30 dB below the desired signal. For PSK signals, especially when idling (not actively transmitting data), IMD should be very low to avoid interference. -30 dB IMD means the distortion products are 30 dB below the signal level, which is acceptable for clean operation. Higher IMD levels (like +5 dB, +10 dB, or +15 dB) would be terrible - they would mean distortion products are stronger than or equal to the signal, which is completely unacceptable. For good signal quality, IMD should be well below the signal level (negative dB values).
考试技巧
PSK IMD maximum = -30 dB. Remember: Acceptable maximum IMD for an idling PSK signal is -30 dB (distortion 30 dB below signal). Positive IMD values are unacceptable.
记忆口诀
**P**SK **I**MD **M**ax = **-3**0 **d**B (think 'PIM = -30dB')
实际应用示例
You're testing your PSK signal and measure -35 dB IMD. This is good - the distortion products are 35 dB below your signal level, which is better than the -30 dB maximum. If you measured +5 dB IMD, that would be terrible - distortion stronger than your signal. For clean PSK operation, IMD should be -30 dB or lower.
错误选项分析
Option A: Incorrect. +5 dB IMD would mean distortion products are 5 dB stronger than the signal, which is terrible and completely unacceptable. IMD should be negative (below the signal). Option B: Incorrect. +10 dB IMD would mean distortion is 10 dB stronger than the signal, which is even worse. This is completely unacceptable. Option C: Incorrect. +15 dB IMD would mean distortion is 15 dB stronger than the signal, which is extremely bad. IMD must be negative (below signal level).
知识点
IMD, PSK, Intermodulation distortion, Signal quality
Verified Content
Question from official FCC Extra Class question pool. Explanation reviewed by licensed amateur radio operators.