Discussion
A receiver with \( 3 \ \mathrm{dB} \) noise figure is preceded by \( 1 \ \mathrm{dB} \) of feeder loss. The system noise figure is
Answer: D
A passive loss ahead of the first amplifier adds directly:
\[ 1 + 3 = 4 \ \mathrm{dB} \]
so 4 dB, and a decibel of feeder has cost a decibel of sensitivity. 3 dB ignores the feeder, which is the mistake the Friis formula exists to prevent. 2 dB has the sign wrong. And 6 dB double-counts. The simplicity of this addition is exactly why low-loss feeders and mast-head amplifiers are worth their cost on any weak-signal installation.
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