链路预算计算器 — 公式

## 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.

计算示例

LNA (1.5 dB NF, 20 dB gain) followed by mixer (10 dB NF, 15 dB gain) and IF amp (15 dB NF).

  1. F1 = 10^(1.5/10) = 1.413
  2. F2 = 10^(10/10) = 10, G1 = 10^(20/10) = 100
  3. F3 = 10^(15/10) = 31.62, G2 = 10^(15/10) = 31.62
  4. F_total = 1.413 + (10-1)/100 + (31.62-1)/(100x31.62) = 1.413 + 0.09 + 0.0097 = 1.513
  5. NF = 10 x log10(1.513) = 1.80 dB