Signal To Noise Ratio Analysis

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Register to read the introduction… However, the S/N ratio specification is more meaningful in practical situations. The C/N ratio is commonly used in satellite communications systems to point or align the receiving dish; the best dish alignment is indicated by the maximum C/N ratio. * Graphical representaion of C/N ratio

Signal-to-Noise Ratio * In analog and digital communications, signal-to-noise ratio, often written S/N or SNR, is a measure of signal strength relative to background noise. The ratio is usually measured in decibels (dB). * Signal-to-noise ratio, or SNR, is a measurement that describes how much noise is in the output of a device, in relation to the signal level. * SNR is actually two level measurements, followed by a simple calculation. First, we measure the output level of the device under test with no input signal. Then we apply a signal to the device and take another level measurement. Then we divide.

Signal-to-Noise Ratio
(mathematical approach) * If the incoming signal strength in microvolts is Vs, and the noise level, also in microvolts, is Vn, then the signal-to-noise ratio, S/N, in decibels is given by the formula:
S/N = 20
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* Simply a ratio of input signal-to-noise ratio tooutput signal-to-noise ratio * “Any unwanted input” * Limits systems ability to process weak signals * Sources: * Random noise in resistors and transistors * Mixer noise * Undesired cross-coupling noise * Power supply noise * Dynamic range – capability of detecting weak signals in presence of large-amplitude signals

Noise Factor * IEEE Standards: “The noise factor, at a specified input frequency, is defined as the ratio of (1) the total noise power per unit bandwidth available at the output port when noise temperature of the input termination is standard (290 K) to (2) that portion of (1) engendered at the input frequency by the input termination.” * “noisiness” of the signal measure = signal-to-noise ratio (frequency dependant) * The noise factor F of a system is defined as:
F = (SNRin)/(SNRout) * where * SNRin= input signal-to-noise power ratio * SNRout = output signal-to-noise power ratio

What is Noise

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