Updated: Dec 9, 2025 | Source: 2024-2028 Question Pool | Topic: E4E
E4E05E4E

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

PreviousNext

Deep Dive: E4E05

The correct answer is B: A brute-force AC-line filter in series with the motor's power leads. What is used to suppress radio frequency interference from a line-driven AC motor is a brute-force AC-line filter in series with the motor's power leads. AC-line filters suppress RFI from motors. For amateur radio operators, this is important for reducing interference. Understanding this helps when suppressing RFI.

Why Other Answers Are Wrong

Option A: Incorrect. High-pass filter in series with motor's power leads isn't correct - brute-force AC-line filter is used. High-pass filter isn't the solution. Option C: Incorrect. Bypass capacitor in series with motor's field winding isn't correct - brute-force AC-line filter is used. Series capacitor isn't the solution. Option D: Incorrect. Bypass choke in parallel with motor's field winding isn't correct - brute-force AC-line filter is used. Parallel choke isn't the solution.

Exam Tip

Suppress RFI from AC motor = brute-force AC-line filter in series with motor's power leads. Think 'R'FI from 'A'C 'M'otor = 'B'rute-'F'orce 'A'C-line 'F'ilter. AC-line filters suppress RFI from motors. Not high-pass filter, not series capacitor, not parallel choke - just brute-force AC-line filter.

Memory Aid

Suppress RFI from AC motor = brute-force AC-line filter in series with motor's power leads. Think 'R'FI from 'A'C 'M'otor = 'B'rute-'F'orce filter. AC-line filters suppress RFI from motors. Important for reducing interference.

Real-World Example

Suppressing radio frequency interference from a line-driven AC motor: A brute-force AC-line filter in series with the motor's power leads is used. This filter blocks RF noise from the motor from traveling back on the power line. This is what's used - brute-force AC-line filter.

Source & Coverage

Question Pool: 2024-2028 Question Pool

Subelement: E4E

Reference: 2024-2028 Question Pool · E4 - Amateur Practices

Key Concepts

Radio frequency interference Line-driven AC motor Suppress Brute-force AC-line filter Series with motor's power leads

Verified Content

Question from the official FCC Extra Class pool. Explanation reviewed by licensed amateur radio operators and mapped to the E4E topic.