*Question E7F11:
What sets the minimum detectable signal level for a direct-sampling software defined receiver in the absence of atmospheric or thermal noise?*  

*Correct Answer is  B: Reference voltage level and sample width in bits*  

### AI Response: (may contain errors)  

To understand what sets the minimum detectable signal level for a direct-sampling software-defined receiver in the absence of atmospheric or thermal noise, we need to analyze the options provided.

### Correct Answer: B - Reference voltage level and sample width in bits

- **Explanation**: 
  - The minimum detectable signal level is fundamentally influenced by the reference voltage level and the sample width in bits. The reference voltage determines the range of signal amplitudes that can be accurately represented, while the sample width (bit depth) defines the resolution of the signal. 
  - For example, if you have a 12-bit ADC (Analog-to-Digital Converter), the smallest voltage increment it can detect is determined by the reference voltage divided by $2^{12}$ (4096 levels). Thus, a higher bit depth allows for finer resolution and better detection of weak signals.

### Why the Other Choices are Incorrect:

- **A: Sample clock phase noise**  
  - While phase noise can affect the quality of the signal, it does not set the minimum detectable signal level. Instead, it contributes to the overall noise floor and can degrade the signal quality, but it does not define the threshold for detection.

- **C: Data storage transfer rate**  
  - The data storage transfer rate pertains to how quickly data can be written or read from storage. It does not influence the minimum signal level that can be detected; rather, it affects how much data can be processed in a given time frame.

- **D: Missing codes and jitter**  
  - Missing codes refer to quantization errors that can occur in ADCs, and jitter relates to timing variations in the sampling process. While these factors can introduce errors and affect signal integrity, they do not set the minimum detectable signal level directly.

### Summary

In summary, the minimum detectable signal level in a direct-sampling software-defined receiver is primarily determined by the reference voltage level and the sample width in bits. Understanding these concepts is crucial for optimizing receiver performance and ensuring accurate signal detection.