ARRL Technician Practice Exam

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Question: 1 / 470

What is the approximate change in decibels (dB) for a power decrease from 12 watts to 3 watts?

3 dB

-3 dB

-6 dB

To find the approximate change in decibels (dB) for a power decrease from 12 watts to 3 watts, you can use the formula for calculating the change in decibels due to a change in power:

\[ \Delta dB = 10 \times \log_{10} \left( \frac{P2}{P1} \right) \]

where $ P1 $ is the initial power level (12 watts) and $ P2 $ is the final power level (3 watts).

Substituting the values gives:

\[ \Delta dB = 10 \times \log_{10} \left( \frac{3}{12} \right) \]

\[ \Delta dB = 10 \times \log_{10} \left( 0.25 \right) \]

Calculating the logarithm:

The logarithm of 0.25 is -0.602. Therefore,

\[ \Delta dB = 10 \times (-0.602) = -6.02 \text{ dB} \]

This value is approximately -6 dB. This indicates a decrease in power level, which is consistent with the concept that a decrease in power

ARRL Technician Practice Exam

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