<Dl> <Dd> F = F 1 + F 2 − 1 G 1 + F 3 − 1 G 1 G 2 + F 4 − 1 G 1 G 2 G 3 + ⋯ + F n − 1 G 1 G 2 G 3 ⋯ G n − 1, (\ displaystyle F = F_ (1) + (\ frac (F_ (2) - 1) (G_ (1))) + (\ frac (F_ (3) - 1) (G_ (1) G_ (2))) + (\ frac (F_ (4) - 1) (G_ (1) G_ (2) G_ (3))) + \ cdots + (\ frac (F_ (n) - 1) (G_ (1) G_ (2) G_ (3) \ cdots G_ (n - 1))),) </Dd> </Dl> <Dd> F = F 1 + F 2 − 1 G 1 + F 3 − 1 G 1 G 2 + F 4 − 1 G 1 G 2 G 3 + ⋯ + F n − 1 G 1 G 2 G 3 ⋯ G n − 1, (\ displaystyle F = F_ (1) + (\ frac (F_ (2) - 1) (G_ (1))) + (\ frac (F_ (3) - 1) (G_ (1) G_ (2))) + (\ frac (F_ (4) - 1) (G_ (1) G_ (2) G_ (3))) + \ cdots + (\ frac (F_ (n) - 1) (G_ (1) G_ (2) G_ (3) \ cdots G_ (n - 1))),) </Dd> <P> where F is the noise factor for the n - th device, and G is the power gain (linear, not in dB) of the n - th device . The first amplifier in a chain usually has the most significant effect on the total noise figure because the noise figures of the following stages are reduced by stage gains . Consequently, the first amplifier usually has a low noise figure, and the noise figure requirements of subsequent stages is usually more relaxed . </P>

How to calculate noise figure of a receiver