Introduction To Noise Figure - Keysight Technologies N9040B UXA Manual

Keysight X-Series Signal Analyzers
N9069C Noise Figure
Measurement Guide
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Introduction to Noise Figure

Modern receiving systems must often process very weak signals, but the noise
added by the system components tends to obscure those very weak signals.
Sensitivity, bit error ratio (BER) and noise figure are system parameters that
characterize the ability to process low-level signals. Of these parameters, noise
figure is unique in that it is suitable not only for characterizing the entire
system, but also the system components such as the preamplifier, mixer, and
IF amplifier that make up the system. By controlling the noise figure and gain of
the system components, you can directly control the noise figure of the overall
system. Once the noise figure is known, system sensitivity can be estimated
from the system bandwidth. Noise figure is often the key parameter that
differentiates one system from another, one amplifier from another, and one
transistor from another.
The noise figure of a network is defined to be the ratio of the signal-to-noise
power ratio at the input to the signal-to-noise power ratio at the output.
Noise figure is independent of the modulation format and of the fidelity of
modulators and demodulators. Noise figure is a more general concept than
noise-quieting used to indicate the sensitivity of FM receivers or BER used in
digital communication.
Noise figure should be thought of as separate from gain. Once noise is added
to the signal, subsequent gain amplifies the signal and noise together and
does not change the signal-to-noise ratio.
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