Q) What is the approximate amount of change, measured in decibels (dB), of a power decrease from 12 watts to 3 watts?
A) 6 dB
The following formula will allow you calculate the ratio in decibels given two different power values.
dB = 10 * Log(Pa / Pb)
Using the figures in the question:
dB = 10 * Log (12 / 3)
dB = 10 * Log(4)
dB = 10 * 0.6
dB = 6
This question is from the FCC Element 2 Technician Class Question Pool
Effective July 1, 2010 for examinations and is valid until June 30, 2014