*Question E7H11:
What are the major spectral impurity components of direct digital synthesizers?*  

*Correct Answer is  C: Spurious signals at discrete frequencies*  

### AI Response: (may contain errors)  

To understand the major spectral impurity components of direct digital synthesizers (DDS), let's analyze the correct answer and the other options.

### Correct Answer: C - Spurious signals at discrete frequencies

- **Explanation**: 
  - Direct digital synthesizers generate signals by creating a digital representation of a waveform, which is then converted to an analog signal. 
  - During this process, spurious signals can occur at discrete frequencies due to non-idealities in the digital-to-analog conversion and the quantization process. 
  - These spurious signals are unwanted frequencies that can interfere with the desired output, making them a significant concern in DDS systems.

### Why the Other Choices are Incorrect:

- **A: Broadband noise**  
  - **Explanation**: While broadband noise can be present in any electronic system, it is not a major characteristic of DDS. Instead, it is more associated with thermal noise and other random processes rather than the specific artifacts produced by the DDS process.

- **B: Digital conversion noise**  
  - **Explanation**: Digital conversion noise refers to errors introduced during the conversion from digital to analog signals. While it can affect the output, it is not classified as a major spectral impurity component like spurious signals. It is more of a general term rather than a specific spectral impurity.

- **D: Harmonics of the local oscillator**  
  - **Explanation**: Harmonics are indeed present in many systems, including those using local oscillators. However, in the context of DDS, the primary concern is the spurious signals that arise from the digital synthesis process itself, rather than the harmonics of the local oscillator, which are typically more predictable and manageable.

### Summary

In summary, the major spectral impurity components of direct digital synthesizers are primarily the spurious signals at discrete frequencies, which arise from the digital synthesis process. Understanding these components is crucial for optimizing the performance of DDS systems and minimizing unwanted interference.