How much must the power output of a transmitter be raised to change the S meter reading on a distant receiver from S8 to S9?
Why By convention one S unit equals 6 dB of signal strength change. In power terms, 6 dB is a factor of about 4 (3 dB doubles power, another 3 dB doubles it again), so going from S8 to S9 on the far end requires roughly four times the transmitter output.
Watch out Doubling power is only a 3 dB increase, which is just half an S unit, so the choice that says approximately 2 times falls short; eight times would be about 9 dB, or a unit and a half.
1 S unit = 6 dB = 4x power. Two S units would take 16x.