What is considered an acceptable maximum IMD level for an idling PSK signal?

Intermodulation Distortion (IMD) measures the strength of unwanted spurious emissions compared to the main, desired signal. It is expressed in decibels (dB) relative to the peak envelope power. For an idling PSK signal, the IMD products should be at least 30 decibels weaker than the main signal. Therefore, -30 dB is considered the maximum acceptable level. If the IMD is higher (for example, -20 dB), it indicates the transmitter is being overdriven and the signal is splattering. The distractors featuring positive dB values (+5 dB, +10 dB, +15 dB) are incorrect because a positive value would mean the distortion products are actually stronger than the fundamental signal, which is physically impossible in this context.