How do I convert between noise figure in dB and equivalent noise temperature in Kelvin?
Noise Figure and Noise Temperature Conversion
Noise figure and noise temperature are two representations of the same physical quantity: the noise added by a component or system. The conversion between them is exact, lossless, and always valid. The standard reference temperature T0 = 290 K (approximately 17°C or 62°F) serves as the bridge between the two scales.
| Parameter | Superheterodyne | Direct Conversion | Digital IF |
|---|---|---|---|
| Image Rejection | 60-90 dB (filter) | 30-50 dB (mismatch) | N/A (digital) |
| DC Offset | No issue | Major issue | No issue |
| LO Leakage | Low | High | Low |
| Integration | Difficult | Easy (single chip) | Moderate |
| Dynamic Range | 80-120 dB | 60-90 dB | 70-100 dB |
Frequently Asked Questions
Is 290 K exactly room temperature?
No. 290 K (16.85°C) was chosen by the IEEE as the standard reference temperature for noise calculations. Actual room temperature is closer to 295-300 K, but 290 K is the universal standard used in all noise figure specifications and measurements.
Can noise temperature be negative?
No. A noise temperature of 0 K means the component adds no noise (perfect, noiseless device). Negative noise temperatures have no physical meaning in this context. The minimum noise figure is 0 dB, corresponding to Te = 0 K.
Which should I put on a datasheet?
Industry convention uses noise figure (NF in dB) for component specifications. Noise temperature is used in system-level specifications, particularly for satellite and radio astronomy receivers where G/T is the key figure of merit.