NF
NF
Noise Figure, the measure of degradation in signal-to-noise ratio caused by a component or system, expressed in dB as the ratio of input SNR to output SNR
Understanding NF
Noise figure quantifies how much noise a device adds to a signal. An ideal noiseless device has NF = 0 dB, meaning it degrades the SNR by 0 dB. Practical amplifiers have NF from 0.3 dB (cryogenic LNAs) to 10+ dB (power amplifiers).
NF is related to noise temperature by T = 290(10^(NF/10) - 1). For cascaded stages, the Friis formula shows that the first stage NF dominates the system NF when the first stage has sufficient gain.
Common Questions
Frequently Asked Questions
What is a good noise figure?
For LNAs, 0.5-2 dB is typical. For mixers, 5-8 dB. For receivers, 2-5 dB is common depending on the application.
How is noise figure measured?
NF is measured using the Y-factor method with a calibrated noise source, or directly with a noise figure analyzer.
See Also