Noise Figure Calculator
Calculate the cascaded noise figure of a receiver chain using the Friis formula.
dB
dB
dB
dB
dB
Cascaded Noise Figure
1.80 dB
Total Gain35.0 dB
Noise Temperature148.5 K
Cascaded Noise Figure vs Stage 1 Noise Figure
Friis Noise Figure Formula
Formula
F_total = F1 + (F2 - 1)/G1 + (F3 - 1)/(G1 x G2) + ...
All values in linear (not dB). The first stage dominates overall noise figure. Use a low-noise amplifier (LNA) first for best sensitivity.
Example Calculation
LNA (1.5 dB NF, 20 dB gain) followed by mixer (10 dB NF, 15 dB gain) and IF amp (15 dB NF).
- 01F1 = 10^(1.5/10) = 1.413
- 02F2 = 10^(10/10) = 10, G1 = 10^(20/10) = 100
- 03F3 = 10^(15/10) = 31.62, G2 = 10^(15/10) = 31.62
- 04F_total = 1.413 + (10-1)/100 + (31.62-1)/(100x31.62) = 1.413 + 0.09 + 0.0097 = 1.513
- 05NF = 10 x log10(1.513) = 1.80 dB
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