støyfigur

Støyfigur, or noise figure, is a measure used in electronics and telecommunications to quantify how much a device degrades the signal-to-noise ratio (SNR) of a system. It expresses how much extra noise the device adds relative to an ideal noiseless component. The quantity is commonly reported in linear form as F = SNR_in / SNR_out, and in decibels as NF = 10 log10(F). An ideal noiseless device has NF of 0 dB (F = 1); real devices have NF > 0 dB.

Relation to noise temperature and system performance can be described by NF ≈ 1 + T_e / T_0, where T_0 is a reference temperature (often 290 K) and T_e is the device’s equivalent input noise temperature. A lower støyfigur indicates better sensitivity and lower added noise.

For systems with multiple components, the total noise figure is described by the Friis formula: F_total = F1 + (F2 − 1)/G1 + (F3 − 1)/(G1 G2) + ..., where Fi are the individual noise factors and Gi are the linear power gains of preceding stages. This highlights the importance of an low-noise first stage in a chain.

Measurement and standards: støyfigur is typically measured with a noise figure meter using the Y-factor method, which compares device output with known hot and cold noise sources. Measurements adjust for impedance matching and reference temperature, and are frequency-dependent.

Applications and interpretation: støyfigur is used to evaluate amplifiers, receivers, mixers and other RF front-end components. Lower values indicate less added noise and better sensitivity, which is crucial in satellite, microwave and wireless communications.