Question

Figure shows a communication system. What is the output power when input signal is of 1.01 mW? (gain in dB = 10 log10 (P_o/P_i).

Answer 1

Here, transmission = 5 km

Loss suffered in transmission path = – 2d Bkm^–1 × 5 km = – 10 db

 Total amplifier gain = 10 dB + 20 dB = 30 dB

Over gain of signal = 30 dB – 1 dB = 20 dB

∴ 20 = 10 log₁₀  .....(P₀/P₁)

or log₁₀  .....(P₀/P₁) = `20/10` = 2 = log₁₀ 100 P₀/P_t =100

or P₀ = P_t × 100 = 1.01 mW × 100 = 101 mW.