Make Accurate Sub-1 dB Noise Figure Measurements Part 1: Noise Concepts

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  • Author: Eric Marsan
One of the most important capabilities of a radio receiver is its ability to reliably detect very weak RF signals. The circuits of a radio receiver inevitably generate electrical noise, which may mask the received signal if the receiver is not properly designed to minimize this noise. The accurate measurement of the receiver’s noise performance is of paramount importance in the assessment of its suitability for reliable communications. This concern is compounded by the fact that modern RF systems are increasingly powered by batteries which necessitates the reduction in transmitter output power, which commensurately reduces signal levels at the receiver. Noise figure (NF) is a figure of merit of RF components that describes their noise performance, and is of particular importance in receiver applications. In addition to the voltage standing wave ratio (VSWR) and the gain of the system itself, the measurement of noise figure is affected by numerous environmental factors such as the ambient temperature and the presence of interference.