1.

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)))

Answer»

90mW
101mW
1112mW
120mW

Solution :
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`


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