*Question T7B03:
Which of the following can cause radio frequency interference?*  

*Correct Answer is  D: All these choices are correct*  

### AI Response: (may contain errors)  

To understand why the correct answer is "All these choices are correct," let's break down each option:

1. **Fundamental overload**:  
   - This occurs when a transmitter operates at a power level that exceeds the linear range of the amplifier or other components. This can lead to distortion and unwanted signals, causing interference with other radio frequencies.

2. **Harmonics**:  
   - Harmonics are signals that are integer multiples of the fundamental frequency. For example, if a transmitter operates at a frequency of $f$, the second harmonic would be at $2f$, the third at $3f$, and so on. These harmonics can radiate and interfere with other communications, especially if they fall within the same band as other users.

3. **Spurious emissions**:  
   - Spurious emissions are unwanted signals that are not harmonics of the fundamental frequency. They can arise from non-linearities in the transmitter or from other components in the system. These emissions can occur at various frequencies and can cause interference with other radio services.

Since all three options can indeed cause radio frequency interference, the correct answer is:

**D: All these choices are correct.**

### Summary:
- **Fundamental overload** leads to distortion and unwanted signals.
- **Harmonics** are multiples of the fundamental frequency that can interfere with other signals.
- **Spurious emissions** are unwanted signals that can occur at various frequencies.

### Useful Rule of Thumb:
To minimize interference:
- Ensure your transmitter is operating within its specified power range.
- Use filters to reduce harmonics and spurious emissions.
- Regularly check and maintain your equipment to prevent unwanted signals.