Discussion
A feeder with \( 3 \ \mathrm{dB} \) loss precedes a receiver of \( 3 \ \mathrm{dB} \) noise figure. The system noise figure is about
Answer: C
A passive loss ahead of the receiver adds its own decibels to the noise figure, so
\[ NF = 3 + 3 = 6 \ \mathrm{dB} \]
giving about 6 dB, which is why feeder loss at the front of a system is so damaging and why the amplifier is moved to the antenna. Keeping the receiver's own 3 dB ignores the feeder. 4.5 dB averages them. And 9 dB double-counts. That a passive component can dominate a noise budget surprises people until they apply the formula.
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