*Question E8D09:
What is considered an acceptable maximum IMD level for an idling PSK signal?*  

*Correct Answer is  D: -30 dB*  

### AI Response: (may contain errors)  

In the context of PSK (Phase Shift Keying) signals, Intermodulation Distortion (IMD) is an important factor to consider. IMD occurs when unwanted mixing products are generated in a non-linear system, such as an amplifier, and can interfere with the desired signal.

### Explanation:

1. **Correct Answer: D: -30 dB**

   - An acceptable maximum IMD level for an idling PSK signal is typically **-30 dB**. This means that the intermodulation products should be at least 30 dB below the level of the desired signal. A lower IMD level (more negative) indicates better signal quality and less interference from unwanted mixing products.

2. **Why the Other Choices are Incorrect:**

   - **A: +5 dB**  
     An IMD level of +5 dB would mean that the intermodulation products are stronger than the desired signal, which is unacceptable as it would cause significant interference.

   - **B: +10 dB**  
     Similar to +5 dB, an IMD level of +10 dB indicates that the intermodulation products are even stronger than the desired signal, leading to severe interference.

   - **C: +15 dB**  
     An IMD level of +15 dB is even worse, with intermodulation products being much stronger than the desired signal, which is highly undesirable.

### Key Points:

- **IMD Level**: The IMD level is expressed in decibels (dB) relative to the desired signal. A negative value indicates that the intermodulation products are weaker than the desired signal, which is preferred.

- **Rule of Thumb**: For high-quality communication, especially in digital modes like PSK, maintaining a low IMD level (e.g., -30 dB or lower) is crucial to minimize interference and ensure clear signal transmission.

Understanding and controlling IMD is essential for maintaining signal integrity and ensuring efficient use of the radio spectrum.