What is noise temperature?
The equivalent noise temperature Te of a device is the temperature at which a source resistor would have to be to produce the device’s added output noise. It relates to noise factor by Te = T0(F − 1) with T0 = 290 K. An NF of 1 dB equals about 75 K; 3 dB equals about 289 K.[1]
Why use noise temperature instead of noise figure?
Noise temperatures add directly, which is convenient when noise levels are far below 290 K, as in satellite ground stations and radio astronomy. Low-noise amplifiers with NF of 0.3 dB (about 21 K) are easier to compare in kelvin. The cascade formula becomes T = T1 + T2/G1 + T3/(G1G2) + ….[2]
What is system noise temperature?
Tsys = TA + Te,rx, where TA is the antenna noise temperature (sky, ground and loss contributions) and Te,rx the receiver’s. A lossy line of loss L (linear) at physical temperature Tp contributes Te = (L − 1)Tp. The figure of merit for a satellite earth station is G/T in dB/K.[1][3]
What values should you remember?
| NF (dB) | Te (K) |
|---|---|
| 0.5 | 35 |
| 1 | 75 |
| 2 | 170 |
| 3 | 289 |
| 6 | 865 |
| 10 | 2,610 |
Frequently asked questions
How do I convert NF to noise temperature?
T = 290·(10^(NF/10) − 1) kelvin.
What is antenna noise temperature?
The temperature of a matched resistor that would deliver the same noise power as the antenna sees from its surroundings.
What is G/T?
Antenna gain divided by system noise temperature, in dB/K; a receive-station figure of merit.
See also
References
Online sources accessed October 21, 2026; printed works cited by edition. See all sources.
- “Microwave Engineering, 4th ed.”. D. M. Pozar, Wiley. 2012.
- “Noise Figures of Radio Receivers”. H. T. Friis, Proceedings of the IRE, vol. 32, no. 7, pp. 419-422. July 1944.
- “Recommendation ITU-R P.372: Radio noise”. ITU-R. current version.