Noise Figure Calculator
Calculate cascaded noise figure using the Friis formula for RF systems.
Typical Noise Figures
| Component | NF (dB) | Notes |
|---|---|---|
| Low-noise LNA | 0.3-1.0 | GaAs, GaN |
| Standard LNA | 1.0-2.0 | SiGe |
| Mixer | 5-8 | Conversion loss |
| Cable (per dB loss) | = loss | Before LNA |
| Filter | 0.5-3 | Insertion loss |
Friis Noise Formula
Cascaded Noise Factor
F_total = F1 + (F2-1)/G1 + (F3-1)/(G1*G2) + ...
F = noise factor (linear), G = gain (linear)
F = noise factor (linear), G = gain (linear)
The Friis formula shows that the first stage dominates system noise figure, making a low-noise LNA critical at the front end.
Key Relationships
NF(dB) = 10 * log10(F)
Te = (F - 1) * T0
Noise Floor = -174 + 10*log10(BW) + NF
Te = (F - 1) * T0
Noise Floor = -174 + 10*log10(BW) + NF
- -174 dBm/Hz is thermal noise at 290K
- Lower NF = better sensitivity
- Losses before LNA add directly to NF