📶 Noise Figure Calculator
Enter the input and output signal-to-noise ratios of an amplifier or receiver stage to find its noise figure and equivalent noise temperature.
What This Calculator Does
Noise figure measures how much an amplifier or receiver stage degrades the signal-to-noise ratio (SNR) of a signal passing through it. This calculator finds the noise figure in decibels, the equivalent linear noise factor, and the equivalent noise temperature from the input and output SNR values.
The Formula
Noise figure in decibels is simply NF (dB) = SNRin (dB) − SNRout (dB), reflecting how much the SNR drops as the signal passes through the stage. Converting to the linear noise factor uses F = 10(NF/10), and the equivalent noise temperature is Te = 290 × (F − 1) kelvin, using the standard reference temperature of 290K (about room temperature).
- Lower noise figure means the stage adds less noise and preserves signal quality better — an ideal, noiseless amplifier has NF = 0dB.
- Cascaded stages combine via the Friis formula, where the first stage’s noise figure dominates the overall system noise figure.
This is the standard definition used in RF and communications engineering education and general system planning; real-world measurements require calibrated test equipment and controlled bandwidth conditions.