*Question E4E05:
What is used to suppress radio frequency interference from a line-driven AC motor?*  

*Correct Answer is  B: A brute-force AC-line filter in series with the motor’s power leads*  

### AI Response: (may contain errors)  

To suppress radio frequency interference (RFI) from a line-driven AC motor, a brute-force AC-line filter is used. Here's why:

### Correct Answer: B

- **Brute-force AC-line filter**: This type of filter is designed to block or attenuate unwanted radio frequency signals while allowing the desired AC power to pass through. It typically consists of inductors and capacitors that work together to filter out high-frequency noise. By placing this filter in series with the motor's power leads, it effectively reduces RFI emissions from the motor.

### Why Other Choices Are Incorrect:

- **Choice A: High-pass filter in series with the motor’s power leads**  
  A high-pass filter allows high-frequency signals to pass while blocking low-frequency signals. This is the opposite of what is needed to suppress RFI from an AC motor, as we want to block high-frequency noise, not pass it.

- **Choice C: Bypass capacitor in series with the motor’s field winding**  
  A bypass capacitor is typically used to shunt high-frequency noise to ground, but placing it in series with the motor's field winding would disrupt the motor's operation. Capacitors in series with power lines are not effective for filtering RFI.

- **Choice D: Bypass choke in parallel with the motor’s field winding**  
  A choke is an inductor used to block high-frequency AC signals while allowing DC or low-frequency AC to pass. However, placing it in parallel with the motor's field winding would not effectively suppress RFI from the power leads.

### Key Points:

- **Brute-force AC-line filters** are specifically designed to handle the power levels of AC motors and effectively reduce RFI.
- **Filtering RFI** involves blocking high-frequency noise while allowing the desired power frequency to pass, which is achieved by the combination of inductors and capacitors in the filter.

Understanding the purpose and function of different types of filters is crucial for selecting the correct method to suppress RFI in various applications.