Deep Dive: E4E12
The correct answer is A: Switch-mode power supplies. What causes interference received as a series of carriers at regular intervals across a wide frequency range is switch-mode power supplies. Switch-mode power supplies generate harmonics at regular intervals. For amateur radio operators, this is important for troubleshooting interference. Understanding this helps when identifying interference sources.
Why Other Answers Are Wrong
Option B (Radar transmitters): Incorrect. Radar transmitters don't cause carriers at regular intervals - switch-mode power supplies do. Radar isn't the cause. Option C (Wireless security camera transmitters): Incorrect. Security camera transmitters don't cause carriers at regular intervals - switch-mode power supplies do. Security cameras isn't the cause. Option D (Electric fences): Incorrect. Electric fences don't cause carriers at regular intervals - switch-mode power supplies do. Electric fences isn't the cause.
Exam Tip
Interference as carriers at regular intervals = switch-mode power supplies. Think 'S'witch-'M'ode 'P'ower 'S'upplies = 'S'eries of 'M'ultiple 'P'ower 'S'upply harmonics. Switch-mode power supplies generate harmonics at regular intervals. Not radar, not security cameras, not electric fences - just switch-mode power supplies.
Memory Aid
Interference as carriers at regular intervals = switch-mode power supplies. Think 'S'witch-'M'ode = 'S'eries of 'M'ultiple harmonics. Switch-mode power supplies generate harmonics at regular intervals. Important for troubleshooting interference.
Real-World Example
Interference received as a series of carriers at regular intervals across a wide frequency range: It's caused by switch-mode power supplies. These power supplies switch at high frequencies and generate harmonics at regular intervals (multiples of the switching frequency). This is the cause - switch-mode power supplies.
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.