Question T5B10
From subelement T5 - T5B
Which decibel value most closely represents a power decrease from 12 watts to 3 watts?
Why is this correct?
The correct answer is -6 dB because it represents a 4:1 power ratio. Going from 12 watts to 3 watts means the power is reduced by a factor of 4 (12 ÷ 3 = 4). In decibel terms, -6 dB corresponds to a 4:1 reduction ratio. The other options don't match: -1 dB would be a much smaller decrease, -3 dB represents halving the power (2:1 ratio), and -9 dB would represent an even larger reduction than what occurred.
Memory tip
Remember the key decibel benchmarks: -3 dB = half power, -6 dB = quarter power, -10 dB = one-tenth power. When you see power ratios, divide the original by the final to find the reduction factor, then match it to these standard dB values.
Learn more
In practical amateur radio operation, understanding these power ratios helps evaluate transmission line losses, amplifier gains, and antenna system performance. A -6 dB loss in your feedline means you're losing 75% of your transmitter power before it reaches the antenna. This is why low-loss coax and proper impedance matching are crucial for efficient RF transmission and maximum effective radiated power.
Think about it
Why do you think amateur radio operators use logarithmic decibel scales instead of simple power ratios when discussing signal strength and system gains?