Question

A receiver requires 10 nW as input power. If all the system losses add up to 50dB, then how much power is required from the source?

Answer 1

here, the power required by the receiver is the output power and that required from the source is input power.

Gain in dB=10 log(output power/input power)

we have, loss in dB = -gain in dB = 10 log(input power/output power)

or, 50 = 10 log(input power/10nW)

or, anti-log(5) = input power/10 nW

so the power required from the source is antilog(5)*10nW = 1 mW