- Noise figure
Noise figure (NF) is a measure of degradation of the signal-to-noise ratio (SNR), caused by components in a radio frequency (RF) signal chain. The noise figure is defined as the ratio of the output noise power of a device to the portion thereof attributable to thermal noise in the input termination at standard noise temperature T0 (usually 290 K). The noise figure is thus the ratio of actual output noise to that which would remain if the device itself did not introduce noise. It is a number by which the performance of a radio receiver can be specified.
The noise figure is the difference in decibels (dB) between the noise output of the actual receiver to the noise output of an “ideal” receiver with the same overall gain and bandwidth when the receivers are connected to matched sources at the standard noise temperature T0 (usually 290 K). The noise power from a simple load is equal to kTB, where k is Boltzmann's constant, T is the absolute temperature of the load (for example a resistor), and B is the measurement bandwidth.
This makes the noise figure a useful figure of merit for terrestrial systems where the antenna effective temperature is usually near the standard 290 K. In this case, one receiver with a noise figure say 2 dB better than another, will have an output signal to noise ratio that is about 2 dB better than the other. However, in the case of satellite communications systems, where the antenna is pointed out into cold space, the antenna effective temperature is often colder than 290 K. In these cases a 2 dB improvement in receiver noise figure will result in more than a 2 dB improvement in the output signal to noise ratio. For this reason, the related figure of effective noise temperature is therefore often used instead of the noise figure for characterizing satellite-communication receivers and low noise amplifiers.
In heterodyne systems, output noise power includes spurious contributions from image-frequency transformation, but the portion attributable to thermal noise in the input termination at standard noise temperature includes only that which appears in the output via the principal frequency transformation of the system and excludes that which appears via the image frequency transformation.
The noise factor of a system is defined as:
where SNRin and SNRout are the input and output power signal-to-noise ratios, respectively. The noise figure is defined as:
where SNRin,dB and SNRout,dB are in decibels (dB). The noise figure is the noise factor, given in dB:
These formulae are only valid when the input termination is at standard noise temperature T0, although in practice small differences in temperature do not significantly affect the values.
The noise factor of a device is related to its noise temperature Te:
Attenuators have a noise factor F equal to their attenuation ratio L when their physical temperature equals T0. More generally, for an attenuator at a physical temperature T, the noise temperature is Te = (L − 1)T, giving a noise factor of:
If several devices are cascaded, the total noise factor can be found with Friis' Formula:
where Fn is the noise factor for the n-th device and Gn is the power gain (linear, not in dB) of the n-th device. In a well designed receive chain, only the noise factor of the first amplifier should be significant.
- Noise (electronic)
- Noise figure meter
- Noise level
- Thermal noise
- Signal-to-noise ratio
- Noise Figure Calculator 2- to 30-Stage Cascade
- Noise Figure and Y Factor Method Basics and Tutorial
Noise (in physics and telecommunications) General Noise in... Class of noise Engineering terms RatiosCarrier-to-noise ratio (C/N) · Carrier-to-receiver noise density (C/kT) · dBrnC · Eb/N0 (energy per bit to noise density) · Es/N0 (energy per symbol to noise density) · Modulation error ratio (MER) · Signal, noise and distortion (SINAD) · Signal-to-interference ratio (S/I) · Signal-to-noise ratio (S/N, SNR) · Signal to noise ratio (imaging) · Signal-to-noise plus interference (SNIR) · Signal-to-quantization-noise ratio (SQNR) Related topics
Wikimedia Foundation. 2010.
Look at other dictionaries:
noise figure — triukšmo faktorius statusas T sritis Standartizacija ir metrologija apibrėžtis Dydis, lygus stiprintuvo ar kitokio radioelektroninio įtaiso išėjimo triukšmo visuminės galios ir jos dalies, kurią sukuria signalo šaltinio triukšmas, dalmeniui.… … Penkiakalbis aiškinamasis metrologijos terminų žodynas
noise figure — triukšmo faktorius statusas T sritis fizika atitikmenys: angl. noise factor; noise figure vok. Geräuschverhältnis, n; Rauchfaktor, m rus. коэффициент шума, m; шумфактор, m pranc. facteur de bruit, m … Fizikos terminų žodynas
noise figure — noun see noise factor … Useful english dictionary
Noise Figure — Die Rauschzahl, manchmal auch Rauschfaktor genannt, ist in der Nachrichtentechnik eine Kennzahl bezüglich des Rauschens eines Vierpols. Ein Vierpol, auch als Zweitor bezeichnet, kann in diesem Zusammenhang beispielsweise eine Verstärkerstufe… … Deutsch Wikipedia
Noise-figure meter — A noise figure meter is an instrument for measuring the noise figure of an amplifier, mixer, or similar device. An example instrument is the 1983 era Agilent 8970A. Contents 1 Measurement methods 2 Noise source 2.1 Thermal noise … Wikipedia
Noise (disambiguation) — Noise is unwanted sound or signal. Noise may also refer different types of interference such as: Noise (audio), residual low level hiss or hum Noise (video), snow on video or television pictures Image noise, related to digital photography Noise… … Wikipedia
Noise shaping — is a technique typically used in digital audio, image, and video processing, usually in combination with dithering, as part of the process of quantization or bit depth reduction of a digital signal. Its purpose is to increase the apparent signal… … Wikipedia
Noise (audio) — Noise in audio, recording, and broadcast systems refers to the residual low level sound (usually hiss and hum) that is heard in quiet periods of a programme. In audio engineering, it can refer either to the acoustic noise from loudspeakers, or to … Wikipedia
Noise measurement — is carried out in various fields. In acoustics, it can be for the purpose of measuring environmental noise, or part of a test procedure using white noise, or some other specialised form of test signal. In electronics it relates to the sensitivity … Wikipedia
Figure — may refer to:*A shape, drawing, or representation *Figure 8 *A person s figure *Miniature representation of something **Action figure, in arts *a number *a type of person, as in Christ figureWriting *a figure in writing is a type of floating… … Wikipedia