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→Formula for Noise Figure of a System
Noise figure of a component has been defined above. But one can also define the noise figure of a system consisting of multiple components connected in series. NF of this kind of system is define in a very similar way as above with SNRin is the SNR of input to the system and SNRout is the SNR of the output of the system. <br \>
If we know the individual noise figures, we can calculate the noise figure of the system using this formula,
[[File:NFsystemAmp4.pnggif|frame|center]]where Fn is the noise factor for the n-th device, and Gn is the power gain (linear, not in dB) of the n-th device.
=== Need of LNA ===