Calcolatore Link Budget
Calcola il bilancio di collegamento RF considerando potenza, guadagni e perdite.
Cascaded Noise Figure
1.80 dB
Cascaded Noise Figure vs Stage 1 Noise Figure
Formula
## 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.
Esempio Risolto
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
Domande Frequenti
Why is the first stage so important?
Noise from later stages is divided by the gain of preceding stages. High first-stage gain makes subsequent noise negligible.
What is a good LNA noise figure?
Below 1 dB for satellite receivers. 1-3 dB for typical RF systems. Above 3 dB is considered noisy.
Loss before the LNA?
Any loss (cable, filter) before the LNA adds directly to the noise figure. A 3 dB cable loss adds 3 dB to system NF.
Impara