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In the above formula, P is measured in units of power, such as watts (W) or milliwatts (mW), and the signal-to-noise ratio is a pure number. However, when the signal and noise are measured in volts (V) or amperes (A), which are measures of amplitude, [note 1] they must first be squared to obtain a quantity proportional to power, as shown below:
The noise power from a simple load is equal to kTB, where k is the Boltzmann 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 ...
The noise equivalent bandwidth (or equivalent noise bandwidth (enbw)) of a system of frequency response is the bandwidth of an ideal filter with rectangular frequency response centered on the system's central frequency that produces the same average power outgoing () when both systems are excited with a white noise source. The value of the ...
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.
Cosmic noise has been observed in a range from 8 MHz to 1.43 GHz, the latter frequency corresponding to the 21-cm hydrogen line. Apart from man-made noise, it is the strongest component over the range of about 20 to 120 MHz.
The carrier-to-receiver noise density ratio is usually expressed in dB-Hz. The noise power density, N 0 =kT, is the receiver noise power per hertz, which can be written in terms of the Boltzmann constant k (in joules per kelvin) and the noise temperature T (in kelvins).
Thus, receivers with a narrow bandwidth have a higher sensitivity than receivers with a large bandwidth and input noise can be decreased by cooling the receiver input stage. A noise diode is a device which has a defined excess noise ratio (ENR). When the diode is off (unpowered) the noise from it will be thermal noise defined by the above formula.
For thermal noise, its spectral density is given by N 0 = kT, where k is the Boltzmann constant in joules per kelvin, and T is the receiver system noise temperature in kelvins. The noise amplitude spectral density is the square root of the noise power spectral density, and is given in units such as V / H z {\displaystyle \mathrm {V} /{\sqrt ...