E.10Noise Figure Cascade
Enter the gain and noise figure of each stage in order; empty stages are ignored.
Results
- Total noise figure
- —
- Total gain
- —
- Noise temperature
- —
- Noise floor
- —
- Sensitivity
- —
- Stages used
- —
Formulas
- Friis
- F = F₁ + (F₂ − 1)/G₁ + (F₃ − 1)/(G₁G₂) + … (F, G linear)
- Noise temperature
- T_e = (F − 1) · 290 K
- Sensitivity
- S = −174 dBm/Hz + NF + 10·log₁₀(B) + SNR
Why the first stage matters
In the Friis formula, the noise contribution of later stages is divided by the gain of the preceding stages. The first stage therefore dominates the total noise figure: placing a high-gain, low-noise LNA first reduces the impact of lossy, noisy stages behind it. Any loss between antenna and LNA (cable, filter) adds directly to the total NF.
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