Figure shows a communication system. What is the output power when input is 1.01 mW? (Gain in `dB=10"log"_(10)(P_(o))/(P_(i))`)

Options

A. 90mW
B. 101mW
C. 1112mW
D. 120mW

Answer

B

Explanation

Here, transmission path =5km
Loss suffered in transmission path
`=-2dB km^(-1)xx5km=-10dB`
Total amplifier gain =10dB+20dB=3 0dB
Overall gain of singal =30dB-10dB=20dB
As, gain in `dB=10"log"_(10)((P_(0))/(P_(i))): therefore 20=10"log"_(10)((P_(0))/(P_(i)))`
or `"log"_(10)((P_(0))/(P_(i)))=(20)/(10)=2="log"_(10)100` or `(P_(0))/(P_(i))=100`
or `P_(0)=P_(i)xx100=1.01 mWxx100=101mW`