*Question E4C07:
What does the MDS of a receiver represent?*  

*Correct Answer is  B: The minimum discernible signal*  

### AI Response: (may contain errors)  

The correct answer is B: The minimum discernible signal.

### Explanation:

1. **Why the correct answer is correct:**
   - **Minimum Discernible Signal (MDS):** This is a measure of the weakest signal that a receiver can detect above the noise floor. It is a critical parameter for evaluating the sensitivity of a receiver. The MDS is typically expressed in decibels relative to 1 milliwatt (dBm). A lower MDS value indicates a more sensitive receiver, capable of detecting weaker signals.

2. **Why the other choices are incorrect:**
   - **A: The meter display sensitivity:** This is not related to MDS. Meter display sensitivity refers to how sensitive a meter is to changes in the parameter it measures, such as signal strength.
   - **C: The modulation distortion specification:** This refers to how much distortion is introduced to a signal during modulation, not the sensitivity of the receiver.
   - **D: The maximum detectable spectrum:** This would refer to the range of frequencies a receiver can process, not the sensitivity to weak signals.

### Useful Formula:

- The MDS can be calculated using the formula:  
  $$ \text{MDS (dBm)} = \text{Noise Floor (dBm)} + \text{SNR (dB)} $$
  - **Noise Floor:** The level of background noise in the receiver.
  - **SNR (Signal-to-Noise Ratio):** The minimum SNR required for the signal to be discernible.

Understanding MDS helps in assessing how well a receiver can perform in weak signal conditions, which is crucial for effective communication in amateur radio operations.