Deep Dive: E4E10
The correct answer is D: All these choices are correct. Which of the following can create intermittent loud roaring or buzzing AC line interference includes: arcing contacts in a thermostatically controlled device, a defective doorbell or doorbell transformer inside a nearby residence, and a malfunctioning illuminated advertising display. All three can create this interference. For amateur radio operators, this is important for troubleshooting interference. Understanding this helps when identifying interference sources.
Why Other Answers Are Wrong
Option A: While correct, this is incomplete. Defective doorbell and malfunctioning display can also create this interference. Option B: While correct, this is incomplete. Arcing contacts and malfunctioning display can also create this interference. Option C: While correct, this is incomplete. Arcing contacts and defective doorbell can also create this interference.
Exam Tip
All three can create intermittent loud roaring/buzzing AC line interference: arcing contacts, defective doorbell, malfunctioning display. When all listed sources can create this interference, 'all of the above' is usually the answer. All are valid interference sources.
Memory Aid
All three can create intermittent loud roaring/buzzing AC line interference: Arcing contacts, Defective doorbell, Malfunctioning display. Think 'A'll 'A'C 'I'nterference sources. All three are valid interference sources. Important for troubleshooting interference.
Real-World Example
Intermittent loud roaring or buzzing AC line interference: It can be created by arcing contacts in a thermostatically controlled device, a defective doorbell or doorbell transformer inside a nearby residence, and a malfunctioning illuminated advertising display. All three can cause this type of interference. This is what can create it - all these sources.
Source & Coverage
Question Pool: 2024-2028 Question Pool
Subelement: E4E
Reference: 2024-2028 Question Pool · E4 - Amateur Practices
Key Concepts
Verified Content
Question from the official FCC Extra Class pool. Explanation reviewed by licensed amateur radio operators and mapped to the E4E topic.