Equivalent Noise Temperature

Formula

Description

Equivalent noise temperature provides an alternative way to express the noise contribution of a component by stating what temperature a matched resistor at the input would need to be to produce the same amount of noise. A perfect noiseless amplifier has Te = 0K. The standard reference temperature is T0 = 290K. This representation is preferred in radio astronomy and satellite communications where system noise temperatures are very low (cryogenic LNAs achieve Te < 10K). Noise temperature adds directly for cascaded stages (when properly referred to the same point).

Variables

• Te — Equivalent noise temperature (K)
• T0 — Reference temperature, standard 290K (K)
• NF — Noise factor (linear, not dB)

Practical Notes

A 1 dB noise figure corresponds to Te = 75K. A 3 dB NF gives Te = 290K. Satellite LNAs operate at 40-70K noise temperature (0.5-0.8 dB NF). Radio telescopes use cryogenic receivers at 5-15K. The sky noise temperature at microwave frequencies is about 3K (cosmic microwave background) plus atmospheric contributions.