Noise Figure Calculator

Noise Figure and SNR

Noise figure (NF) measures how much an amplifier or receiver degrades signal-to-noise ratio (SNR). Lower NF means less added noise. RF engineers use NF to compare LNAs, mixers, and receiver chains.

Formulas

In decibels:

$$NF_{dB} = SNR_{in,dB} - SNR_{out,dB}$$

Linear noise factor:

$$F = \frac{SNR_{in}}{SNR_{out}} = 10^{NF_{dB}/10}$$

SNR values here are power ratios expressed in dB. A 10 dB noise figure means the output SNR is 10 dB worse than the input SNR.

Practical Notes

Cascade analysis uses Friis formula for multiple stages. The first low-noise stage dominates system NF, which is why an LNA is placed close to the antenna. Always use consistent bandwidth when comparing SNR values.

Related tools: Op-Amp Gain Calculator and Pi Attenuator Calculator.

Frequently Asked Questions

What is a good noise figure?

LNAs often achieve 0.5–2 dB NF. Consumer receivers may be 5–10 dB or higher depending on design and frequency.

What is the difference between NF and noise factor?

Noise factor F is the linear SNR ratio. Noise figure NF is F expressed in decibels: NF = 10 log₁₀(F).

Can noise figure be negative?

Physical passive devices have NF ≥ 0 dB. Negative values in calculations usually indicate inconsistent or incorrect SNR inputs.

Are SNR values power or voltage ratios?

In RF, SNR is typically a power ratio. For voltage ratios, multiply the dB difference by 2 when converting.

How do I find output SNR from NF?

Rearrange: SNR_out = SNR_in − NF. This calculator can solve for any of the three variables.

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Noise Figure Calculator

Noise Figure and SNR

Formulas

Practical Notes

Frequently Asked Questions

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