Question T5B09
From subelement T5 - T5B
Which decibel value most closely represents a power increase from 5 watts to 10 watts?
Why is this correct?
3 dB represents a power ratio of 2:1, meaning power doubles. Going from 5 watts to 10 watts is exactly doubling the power (10÷5 = 2), so this is a +3 dB gain. The other options don't match this ratio: 2 dB would be less than doubling, 5 dB has no standard meaning, and 10 dB represents a 10:1 ratio (ten times the power).
Memory tip
Remember the key dB benchmarks: 3 dB = double/half, 6 dB = 4x change, 10 dB = 10x change. When you see power problems, first calculate the ratio (new÷old), then match it to these standard values.
Learn more
The 3 dB doubling rule is fundamental in RF system design. When amateur operators add a 3 dB amplifier, they double their effective radiated power. Similarly, a 3 dB attenuator cuts power in half. This logarithmic relationship means that cascaded gains and losses in transmission lines, amplifiers, and antennas can be calculated by simply adding and subtracting dB values rather than multiplying ratios.
Think about it
Why do you think amateur radio operators prefer using decibels instead of just stating power ratios directly when discussing signal strength improvements?