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Signal-to-Noise Ratio (SNR) Calculator

Calculate signal-to-noise ratio, noise floor, receiver sensitivity, and dynamic range for RF systems. Analyze your signal chain performance. Free, instant results.

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Formula

Nfloor=kTB+NF,SNR=Psignal−NfloorN_floor = kTB + NF, SNR = P_signal - N_floor

Reference: Friis, 'Noise Figures of Radio Receivers', Proc. IRE, 1944

k— Boltzmann constant (J/K)
T— Temperature (K)
B— Bandwidth (Hz)
NF— Noise figure (dB)
SNR— Signal-to-noise ratio (dB)

How It Works

The SNR Calculator computes signal-to-noise ratio and receiver noise floor — essential for RF link budget analysis, radar system design, and wireless communication planning. RF engineers, wireless system architects, and test technicians use this to determine receiver sensitivity and predict communication range. According to Shannon's channel capacity theorem (1948), SNR directly limits maximum data rate: a 10 dB SNR improvement doubles achievable throughput. The thermal noise floor follows N = kTB, where k = 1.380649e-23 J/K (2019 SI exact Boltzmann constant), T = absolute temperature, and B = bandwidth. At 290K reference temperature, thermal noise density is -174 dBm/Hz — the fundamental limit for any receiver. Modern LTE receivers achieve 6-8 dB noise figures, while satellite LNBs reach 0.5-1.0 dB. Per Proakis "Digital Communications" (5th ed., Ch. 5), a 3 dB SNR improvement reduces bit error rate by approximately one order of magnitude for QPSK modulation.

Worked Example

A 5G NR base station receiver operates at 3.5 GHz with 100 MHz bandwidth and 5 dB noise figure. Calculate the noise floor and required signal level for 20 dB SNR. Step 1: Thermal noise = -174 + 10*log10(100e6) = -174 + 80 = -94 dBm. Step 2: Effective noise floor = -94 + 5 dB NF = -89 dBm. Step 3: Required signal = -89 + 20 = -69 dBm for 20 dB SNR. This matches 3GPP TS 38.104 reference sensitivity requirements for NR FR1. At this SNR, 64-QAM achieves BER < 1e-6 without coding, enabling 150 Mbps throughput per 100 MHz channel per Proakis Table 5.3.

Practical Tips

  • ✓Per IEEE 1139-2008, always measure noise figure at 290K reference temperature for comparable specifications
  • ✓Use low-noise amplifiers with NF < 1 dB for satellite and radio astronomy applications per ITU-R SA.509
  • ✓Add 3-6 dB implementation margin above theoretical sensitivity for production variations (industry standard practice)

Common Mistakes

  • ✗Using room temperature (300K) instead of IEEE standard 290K reference — causes 0.15 dB error in noise calculations
  • ✗Neglecting noise figure when calculating sensitivity — a 6 dB NF degrades sensitivity by exactly 6 dB
  • ✗Ignoring cable and connector losses before LNA — 1 dB loss before a 2 dB NF LNA raises system NF to 2.8 dB per Friis formula

Frequently Asked Questions

Noise power scales linearly with bandwidth: doubling bandwidth raises noise floor by exactly 3.01 dB. A 10x bandwidth increase adds 10 dB to noise floor. Per Shannon-Hartley theorem, wider bandwidth enables higher data rates but requires proportionally stronger signals.
Satellite LNBs: 0.5-1.0 dB. Cellular base stations: 2-4 dB. WiFi receivers: 4-6 dB. GPS receivers: 1.5-2.5 dB. Consumer devices: 6-10 dB. Per Razavi "RF Microelectronics" (2nd ed.), each 1 dB NF improvement extends range by approximately 12% for fixed transmit power.
Yes — thermal noise scales with absolute temperature. Cooling from 290K to 20K (cryogenic LNA) reduces noise by 10*log10(290/20) = 11.6 dB. Radio telescopes use 4K cryogenic systems achieving 3-5K equivalent noise temperature per IEEE MTT-S standards.
Per Pozar "Microwave Engineering" (4th ed., Ch. 11): (1) Use LNA with NF < 1 dB as first stage — dominates system NF per Friis equation. (2) Minimize cable loss before LNA. (3) Reduce bandwidth to minimum required. (4) Cool front-end for cryogenic applications. Each 3 dB sensitivity improvement doubles maximum range.
BPSK: 10.5 dB for BER=1e-6. QPSK: 10.5 dB. 16-QAM: 17 dB. 64-QAM: 23 dB. 256-QAM: 29 dB. Per 3GPP TS 36.101, LTE requires 15.4 dB SNR for 64-QAM MCS 20. WiFi 6 (802.11ax) 1024-QAM needs 35 dB SNR per IEEE 802.11ax-2021 specification.

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