9.6.3 Signal and Noise Propagation through a Chain of Circuits
First, let us consider an amplifier with gain and noise factor . Let be incoming signal power and be incoming noise power. The SNR of the incoming signal is
At point 0 (Figure 9.6.2, left panel) we add the equivalent noise power of the amplifier related to noise factor as shown by (9.6.22). Then we allow both signal and the total noise to propagate through a noise-less amplifier in accordance with above. At the output (point 1) one has an SNR in the form
9.6.26
This SNR is degraded compared to that of the incoming signal (9.6.25) due to the noise generated by the amplifier.
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and noise factor 
. Let 
be incoming signal power and 
be incoming noise power. The SNR of the incoming signal is
related to noise factor 
as shown by (9.6.22). Then we allow both signal and the total noise to propagate through a noise-less amplifier in accordance with above. At the output (point 1) one has an SNR in the form