*Question E4C08:
An SDR receiver is overloaded when input signals exceed what level?*  

*Correct Answer is  D: The reference voltage of the analog-to-digital converter*  

### AI Response: (may contain errors)  

An SDR (Software Defined Radio) receiver can become overloaded when the input signals exceed the reference voltage of the analog-to-digital converter (ADC). Let's break down why this is the correct answer and why the other choices are incorrect.

### Correct Answer: D - The reference voltage of the analog-to-digital converter

1. **Explanation**:  
   - The ADC in an SDR converts analog signals to digital form. It has a specific range of voltages it can handle, defined by its reference voltage.
   - If the input signal exceeds this reference voltage, the ADC cannot accurately convert the signal, leading to distortion and overload.
   - This is similar to "clipping" in audio systems, where signals that are too strong get cut off, resulting in distortion.

### Why the Other Choices are Incorrect:

2. **Choice A: One-half of the maximum sample rate**  
   - The sample rate determines how often the ADC samples the input signal, not the signal level it can handle.
   - Overloading is related to signal amplitude, not how frequently the signal is sampled.

3. **Choice B: One-half of the maximum sampling buffer size**  
   - The sampling buffer size is related to how much data can be temporarily stored, not the amplitude of the input signal.
   - Buffer size affects data handling and processing, not the ADC's ability to handle signal levels.

4. **Choice C: The maximum count value of the analog-to-digital converter**  
   - The maximum count value refers to the digital representation of the highest voltage the ADC can convert, but it is directly tied to the reference voltage.
   - The reference voltage sets the limit for the maximum count value, so exceeding the reference voltage is the root cause of overload.

### Useful Rule of Thumb:

- **ADC Overload**: Always ensure that the input signal amplitude is within the ADC's reference voltage range to prevent overload and distortion.

By understanding the role of the reference voltage in an ADC, you can better manage signal levels and prevent SDR receiver overload.