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Noise Temperature
In electronics, noise temperature is one way of expressing the level of available noise power introduced by a component or source. The power spectral density of the noise is expressed in terms of the temperature (in kelvins) that would produce that level of Johnson–Nyquist noise, thus: :\frac = k_\text T where: * P_\text is the noise power (in W, watts) * B is the total bandwidth (Hz, hertz) over which that noise power is measured * k_\text is the Boltzmann constant (, joules per kelvin) * T is the noise temperature (K, kelvin) Thus the noise temperature is proportional to the power spectral density of the noise, P_\text/ B. That is the power that would be absorbed from the component or source by a matched load. Noise temperature is generally a function of frequency, unlike that of an ideal resistor which is simply equal to the actual temperature of the resistor at all frequencies. Noise voltage and current A noisy component may be modelled as a noiseless component i ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Power Spectral Density
In signal processing, the power spectrum S_(f) of a continuous time signal x(t) describes the distribution of power into frequency components f composing that signal. According to Fourier analysis, any physical signal can be decomposed into a number of discrete frequencies, or a spectrum of frequencies over a continuous range. The statistical average of any sort of signal (including noise) as analyzed in terms of its frequency content, is called its spectrum. When the energy of the signal is concentrated around a finite time interval, especially if its total energy is finite, one may compute the energy spectral density. More commonly used is the power spectral density (PSD, or simply power spectrum), which applies to signals existing over ''all'' time, or over a time period large enough (especially in relation to the duration of a measurement) that it could as well have been over an infinite time interval. The PSD then refers to the spectral energy distribution that would be ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Decibels
The decibel (symbol: dB) is a relative unit of measurement equal to one tenth of a bel (B). It expresses the ratio of two values of a power or root-power quantity on a logarithmic scale. Two signals whose levels differ by one decibel have a power ratio of 101/10 (approximately ) or root-power ratio of 101/20 (approximately ). The strict original usage above only expresses a relative change. However, the word decibel has since also been used for expressing an absolute value that is relative to some fixed reference value, in which case the dB symbol is often suffixed with letter codes that indicate the reference value. For example, for the reference value of 1 volt, a common suffix is " V" (e.g., "20 dBV"). As it originated from a need to express power ratios, two principal types of scaling of the decibel are used to provide consistency depending on whether the scaling refers to ratios of power quantities or root-power quantities. When expressing a power ratio, it ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Noise (electronics)
In electronics, noise is an unwanted disturbance in an electrical signal. Noise generated by electronic devices varies greatly as it is produced by several different effects. In particular, noise is inherent in physics and central to thermodynamics. Any conductor with electrical resistance will generate thermal noise inherently. The final elimination of thermal noise in electronics can only be achieved cryogenically, and even then quantum noise would remain inherent. Electronic noise is a common component of noise in signal processing. In communication systems, noise is an error or undesired random disturbance of a useful information signal in a communication channel. The noise is a summation of unwanted or disturbing energy from natural and sometimes man-made sources. Noise is, however, typically distinguished from interference, for example in the signal-to-noise ratio (SNR), signal-to-interference ratio (SIR) and signal-to-noise plus interference ratio (SNIR) measu ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Noise Spectral Density
In communications, noise spectral density (NSD), noise power density, noise power spectral density, or simply noise density (''N''0) is the power spectral density of noise or the noise power per unit of bandwidth. It has dimension of power over frequency, whose SI unit is watt per hertz (W/Hz), equivalent to watt-second (Ws) or joule (J). It is commonly used in link budgets as the denominator of the important figure-of-merit ratios, such as carrier-to-noise-density ratio as well as ''E''''b''/''N''0 and ''E''''s''/''N''0. If the noise is one-sided white noise, i.e., constant with frequency, then the total noise power ''N'' integrated over a bandwidth ''B'' is ''N'' = ''BN''0 (for double-sided white noise, the bandwidth is doubled, so ''N'' is ''BN''0/2). This is utilized in signal-to-noise ratio calculations. For thermal noise, its spectral density is given by ''N''0 = ''kT'', where ''k'' is the Boltzmann constant in joules per kelvin (J/K), and ''T'' is ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Antenna Efficiency
Antenna ''apertureillumination efficiency is a measure of the extent to which an antenna or array is uniformly excited or illuminated. It is typical for an antenna pertureor array to be intentionally under-illuminated or under-excited in order to mitigate sidelobes and reduce antenna temperature. It is not to be confused with radiation efficiency or antenna efficiency. Definition Antenna pertureillumination efficiency is defined as "The ratio, usually expressed in percent, of the maximum directivity of an antenna pertureto its standard directivity." It is synonymous with normalized directivity. Standard eferencedirectivity is defined as "The maximum directivity from a planar aperture of area A, or from a line source of length L, when excited with a uniform-amplitude, equiphase distribution." Key to understanding these definitions is that "maximum" directivity refers to the direction of maximum radiation intensity, i.e., the main lobe. Therefore, illumination efficie ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Resistor
A resistor is a passive two-terminal electronic component that implements electrical resistance as a circuit element. In electronic circuits, resistors are used to reduce current flow, adjust signal levels, to divide voltages, bias active elements, and terminate transmission lines, among other uses. High-power resistors that can dissipate many watts of electrical power as heat may be used as part of motor controls, in power distribution systems, or as test loads for generators. Fixed resistors have resistances that only change slightly with temperature, time or operating voltage. Variable resistors can be used to adjust circuit elements (such as a volume control or a lamp dimmer), or as sensing devices for heat, light, humidity, force, or chemical activity. Resistors are common elements of electrical networks and electronic circuits and are ubiquitous in electronic equipment. Practical resistors as discrete components can be composed of various compounds and forms. Resisto ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Attenuator (electronics)
An attenuator is a Passivity (engineering), passive wideband, broadband Electronics, electronic device that reduces the Electric power, power of a signal without appreciably distortion, distorting its waveform. An attenuator is effectively the opposite of an amplifier, though the two work by different methods. While an amplifier provides gain (electronics), gain, an attenuator provides loss, or gain less than unity. An attenuator is often referred to as a "pad" in audio electronics. Construction and usage Attenuators are usually Passivity (engineering), passive devices made from simple voltage divider networks. Switching between different resistances forms adjustable stepped attenuators and continuously adjustable ones using potentiometers. For higher frequencies precisely matched low Standing wave ratio, voltage standing wave ratio (VSWR) Electrical resistance, resistance networks are used. Fixed attenuators in circuits are used to lower voltage, Dissipation, dissipate power, ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Low-noise Amplifier
A low-noise amplifier (LNA) is an electronic component that amplifies a very low-power signal without significantly degrading its signal-to-noise ratio (SNR). Any electronic amplifier will increase the power of both the signal and the noise present at its input, but the amplifier will also introduce some additional noise. LNAs are designed to minimize that additional noise, by choosing special components, operating points, and circuit topologies. Minimizing additional noise must balance with other design goals such as power gain and impedance matching. LNAs are found in radio communications systems, Amateur Radio stations, medical instruments and electronic test equipment. A typical LNA may supply a power gain of 100 (20 decibels (dB)) while decreasing the SNR by less than a factor of two (a 3 dB noise figure (NF)). Although LNAs are primarily concerned with weak signals that are just above the noise floor, they must also consider the presence of larger signals tha ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Preamplifier
A preamplifier, also known as a preamp, is an electronic amplifier that converts a weak electrical signal into an output signal strong enough to be noise-tolerant and strong enough for further processing, or for sending to a power amplifier and a loudspeaker. Without this, the final signal would be noisy or distorted. They are typically used to amplify signals from analog sensors such as microphones and pickups. Because of this, the preamplifier is often placed close to the sensor to reduce the effects of noise and interference. Description An ideal preamp will be linear (have a constant gain through its operating range) and have high input impedance (requiring only a minimal amount of current to sense the input signal) and low output impedance (when current is drawn from the output there is minimal change in the output voltage). It is used to boost the signal strength to drive the cable to the main instrument without significantly degrading the signal-to-noise ratio (SNR) ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Black Box
In science, computing, and engineering, a black box is a system which can be viewed in terms of its inputs and outputs (or transfer characteristics), without any knowledge of its internal workings. Its implementation is "opaque" (black). The term can be used to refer to many inner workings, such as those of a transistor, an engine, an algorithm, the human brain, or an institution or government. To analyze an open system with a typical "black box approach", only the behavior of the stimulus/response will be accounted for, to infer the (unknown) ''box''. The usual representation of this "black box system" is a data flow diagram centered in the box. The opposite of a black box is a system where the inner components or logic are available for inspection, which is most commonly referred to as a white box (sometimes also known as a "clear box" or a "glass box"). History The modern meaning of the term "black box" seems to have entered the English language around 1945. In electroni ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Friis Formulas For Noise
Friis formula or Friis's formula (sometimes Friis' formula), named after Danish-American electrical engineer Harald T. Friis, is either of two formulas used in telecommunications engineering to calculate the signal-to-noise ratio of a multistage amplifier. One relates to noise factor while the other relates to noise temperature. The Friis formula for noise factor Friis's formula is used to calculate the total noise factor of a cascade of stages, each with its own noise factor and power gain (assuming that the impedances are matched at each stage). The total noise factor can then be used to calculate the total noise figure. The total noise factor is given as where F_i and G_i are the noise factor and available power gain, respectively, of the ''i''-th stage, and ''n'' is the number of stages. Both magnitudes are expressed as ratios, not in decibels. Consequences An important consequence of this formula is that the overall noise figure of a radio receiver is primari ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Y-factor
The Y-factor method is a widely used technique for measuring the gain and noise temperature of an amplifier. It is based on the Johnson–Nyquist noise of a resistor at two different, known temperatures. Consider a microwave amplifier with a 50-ohm Electrical impedance, impedance with a 50-ohm resistor connected to the amplifier input. If the resistor is at a physical temperature ''T''R, then the Johnson–Nyquist noise power coupled to the amplifier input is ''P''J = ''k''B''T''R''B'', where ''k''B is the Boltzmann constant, and ''B'' is the bandwidth. The noise power at the output of the amplifier (i.e. the noise power coupled to an impedance-matched load that is connected to the amplifier output) is ''P''out = ''Gk''B(''T''R + ''T''amp)''B'', where ''G'' is the amplifier power gain, and ''T''amp is the amplifier noise temperature In electronics, noise temperature is one way of expressing the level of available noise power introduced by a component or source. The powe ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
