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Noise Figure & System Sensitivity

Friis Cascaded NF · Receiver Sensitivity · DAS Uplink Chain

When to use: Use to calculate the cascaded noise figure of a multi-stage receive chain using the Friis formula. Add up to 4 stages (LNA, filters, cable, BDA/receiver). The first stage dominates — a low-noise LNA early in the chain dramatically improves system sensitivity. Output includes total system NF and receiver sensitivity (dBm) for a given bandwidth and required SNR. Critical for DAS uplink design and public safety BDA installations.

Receive Chain (Friis stages in order)

Stage 1

NF dB

Gain dB

Stage 2

NF dB

Gain dB

Stage 3

NF dB

Gain dB

Stage 4

NF dB

Gain dB

Sensitivity Parameters

Channel Bandwidth

dB SNR min

System Noise Figure

1.71

System sensitivity: -116.3 dBm

Stage-by-Stage NF Contribution

After stage 1 (LNA (Low Noise Amp))1.50 dB NF

After stage 2 (Bandpass Filter)1.51 dB NF

After stage 3 (Cable Loss)1.55 dB NF

After stage 4 (Receiver/BDA)1.71 dB NF

System Sensitivity-116.3 dBm

References

Friis: NF_tot = NF1 + (NF2−1)/G1 + …

Sensitivity = kTB + NF + SNR_min

kT = −174 dBm/Hz at 290 K

First stage NF dominates — use LNA first