What dB change represents a factor of two increase or decrease in power?
The correct answer is B: Approximately 3 dB. The dB change that represents a factor of two increase or decrease in power is approximately 3 dB. Each 3 dB represents a 2:1 power ratio (3 dB ≈ 2×). For amateur radio operators, this is a fundamental relationship. Understanding this helps when comparing power levels.
Exam Tip
Factor of 2 power change = approximately 3 dB. Think '2'× power = '3' dB. Each 3 dB represents a 2:1 power ratio. Not 2 dB (1.58×), not 6 dB (4×), not 9 dB (8×) - just 3 dB for 2×.
Memory Aid
"Factor of 2 power change = approximately 3 dB. Think '2'× power = '3' dB. Each 3 dB represents a 2:1 power ratio. Fundamental dB relationship for power comparisons."
Real-World Application
You double your power from 100 watts to 200 watts. This is a 3 dB increase (2:1 power ratio). If you halve power from 200 watts to 100 watts, that's a 3 dB decrease. Each 3 dB represents a factor of 2 change in power.
Key Concepts
Why Other Options Are Wrong
Option A (2 dB): Incorrect. 2 dB is less than 2:1 - 2 dB represents about 1.58:1, not 2:1. 3 dB is needed for 2:1.
Option C (6 dB): Incorrect. 6 dB is too much - 6 dB represents 4:1, not 2:1. 3 dB is for 2:1.
Option D (9 dB): Incorrect. 9 dB is way too much - 9 dB represents about 8:1, not 2:1. 3 dB is for 2:1.
题目解析
The correct answer is B: Approximately 3 dB. The dB change that represents a factor of two increase or decrease in power is approximately 3 dB. Each 3 dB represents a 2:1 power ratio (3 dB ≈ 2×). For amateur radio operators, this is a fundamental relationship. Understanding this helps when comparing power levels.
考试技巧
Factor of 2 power change = approximately 3 dB. Think '2'× power = '3' dB. Each 3 dB represents a 2:1 power ratio. Not 2 dB (1.58×), not 6 dB (4×), not 9 dB (8×) - just 3 dB for 2×.
记忆口诀
Factor of 2 power change = approximately 3 dB. Think '2'× power = '3' dB. Each 3 dB represents a 2:1 power ratio. Fundamental dB relationship for power comparisons.
实际应用示例
You double your power from 100 watts to 200 watts. This is a 3 dB increase (2:1 power ratio). If you halve power from 200 watts to 100 watts, that's a 3 dB decrease. Each 3 dB represents a factor of 2 change in power.
错误选项分析
Option A (2 dB): Incorrect. 2 dB is less than 2:1 - 2 dB represents about 1.58:1, not 2:1. 3 dB is needed for 2:1. Option C (6 dB): Incorrect. 6 dB is too much - 6 dB represents 4:1, not 2:1. 3 dB is for 2:1. Option D (9 dB): Incorrect. 9 dB is way too much - 9 dB represents about 8:1, not 2:1. 3 dB is for 2:1.
知识点
dB, 3 dB, Power ratio, 2:1 ratio
Verified Content
Question from official FCC General Class question pool. Explanation reviewed by licensed amateur radio operators.