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Question # 12 A mixer-stage in a radio receiver has a NF = 20 dB and this mixer-stage is preceded by a preamplifier with a NF = 9 dB. The available power-gain ratio of the amplifier is equal to A. The overall noise figure of the system with reference to the input is 10.44 dB. A signal of power level equal to 5 the power gain of the preamplifier. Hint: Use Friis formula Answer hints: A 15 dB)