Difficulty understanding why the relationship between noise figure and signal to noise ratio can only be used in the first component of a cascade

Thread Starter


Joined Feb 8, 2020
In a cascaded network with components A and B, and a signal to noise ratio at the input of A, in between A and B, and the output of B (SNi, SNt, SNo), why is the noise figure of component B (NFB) not SNt/SNo, but NFA=SNi/SNt and NF total = SNI/SNO?


Joined Feb 14, 2020
Noise figure (NF) and noise factor (F) are measures of degradation of the signal-to-noise ratio (SNR), caused by components in a signal chain. It is a number by which the performance of an amplifier or a radio receiver can be specified, with lower values indicating better performance.
See here for more info https://en.wikipedia.org/wiki/Noise_figure
You can also find some help here https://www.sciencedirect.com/topics/engineering/noise-factor
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