Noise Temperature
Understanding Noise Temperature
Noise temperature provides a more physical and intuitive representation of noise than noise figure, especially for low-noise and cryogenic systems. It directly represents the equivalent thermal noise power contributed by a component.
NF to Noise Temperature Conversion
| NF (dB) | NF (linear) | T_N (K) |
|---|---|---|
| 0.3 | 1.07 | 21 |
| 0.5 | 1.12 | 35 |
| 1.0 | 1.26 | 75 |
| 2.0 | 1.58 | 170 |
| 3.0 | 2.0 | 290 |
| 6.0 | 4.0 | 870 |
| 10.0 | 10.0 | 2610 |
Frequently Asked Questions
What is noise temperature?
Noise temperature = T_0(NF-1). NF = 1 dB: T_N = 75K. NF = 3 dB: T_N = 290K. Preferred for satellite and radio astronomy where components may be cryogenically cooled and 290K reference is not meaningful.
Why use noise temperature instead of NF?
At cryogenic temperatures (15-80K), NF values are very close to 0 dB and hard to distinguish. Noise temperature (e.g., 5K vs 15K vs 50K) is more descriptive. Also, system noise temperature adds linearly (easier calculation).
What is system noise temperature?
T_sys = T_antenna + T_LNA + T_downstream/G_LNA. It includes all noise contributions: antenna (sky noise), LNA, and subsequent stages. G/T = antenna gain / T_sys is the standard system sensitivity figure of merit.