What is the meaning of the term “picket fencing”?
The correct answer is B: Rapid flutter on mobile signals due to multipath propagation. 'Picket fencing' is a term that describes the rapid, fluttery signal variation experienced in mobile operations due to multipath propagation. The signal strength rapidly increases and decreases, creating an effect that sounds like the signal is 'fencing' or chopping.
When you're mobile, your antenna is constantly moving through areas with different multipath conditions. As you move, the multiple signal paths (direct plus reflections) constantly change their phase relationships, causing rapid signal strength variations. This creates the characteristic 'picket fence' effect - the signal rapidly fades in and out, sounding choppy or fluttery. This is a common experience in mobile VHF/UHF operations.
Exam Tip
Picket fencing = Rapid flutter mobile. Remember: Picket fencing is the rapid flutter on mobile signals caused by multipath propagation as you move through different signal path conditions.
Memory Aid
"**P**icket **F**encing = **P**ath **F**lutter (think 'PF = PF' = Path Flutter, rapid multipath variation)"
Real-World Application
You're driving and operating mobile on 2 meters. As you move, your signal to the repeater rapidly fades in and out - strong one moment, weak the next, then strong again. This choppy, fluttery effect is 'picket fencing.' It's caused by multipath - your signal is bouncing off buildings and terrain, and as you move, these paths constantly change, creating rapid signal strength variations.
FCC Part 97.3Key Concepts
Why Other Options Are Wrong
Option A: Incorrect. Picket fencing isn't about alternating transmissions during nets. It's a propagation phenomenon affecting mobile signals.
Option C: Incorrect. Picket fencing isn't a type of ground system. It's a signal variation effect.
Option D: Incorrect. Picket fencing isn't about local vs long-distance. It's specifically about rapid signal variation in mobile operations.
题目解析
The correct answer is B: Rapid flutter on mobile signals due to multipath propagation. 'Picket fencing' is a term that describes the rapid, fluttery signal variation experienced in mobile operations due to multipath propagation. The signal strength rapidly increases and decreases, creating an effect that sounds like the signal is 'fencing' or chopping. When you're mobile, your antenna is constantly moving through areas with different multipath conditions. As you move, the multiple signal paths (direct plus reflections) constantly change their phase relationships, causing rapid signal strength variations. This creates the characteristic 'picket fence' effect - the signal rapidly fades in and out, sounding choppy or fluttery. This is a common experience in mobile VHF/UHF operations.
考试技巧
Picket fencing = Rapid flutter mobile. Remember: Picket fencing is the rapid flutter on mobile signals caused by multipath propagation as you move through different signal path conditions.
记忆口诀
**P**icket **F**encing = **P**ath **F**lutter (think 'PF = PF' = Path Flutter, rapid multipath variation)
实际应用示例
You're driving and operating mobile on 2 meters. As you move, your signal to the repeater rapidly fades in and out - strong one moment, weak the next, then strong again. This choppy, fluttery effect is 'picket fencing.' It's caused by multipath - your signal is bouncing off buildings and terrain, and as you move, these paths constantly change, creating rapid signal strength variations.
错误选项分析
Option A: Incorrect. Picket fencing isn't about alternating transmissions during nets. It's a propagation phenomenon affecting mobile signals. Option C: Incorrect. Picket fencing isn't a type of ground system. It's a signal variation effect. Option D: Incorrect. Picket fencing isn't about local vs long-distance. It's specifically about rapid signal variation in mobile operations.
知识点
Picket fencing, Multipath propagation, Mobile operation, Signal flutter
Verified Content
Question from official FCC Technician Class question pool. Explanation reviewed by licensed amateur radio operators.