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Thermal Noise No = k x T No : noise power density [watt/Hz] k: Boltzmann’ constant = 1.38 x 10 -23 J/K T: temperature [K] Example: Room temperature is usually specified as T = 17 o C, or 290 K. At this temperature the thermal noise power density is
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Thermal Noise No = k x T No : noise power density [watt/Hz] k: Boltzmann’ constant = 1.38 x 10-23 J/K T: temperature [K] Example: Room temperature is usually specified as T = 17o C, or 290 K. At this temperature the thermal noise power density is No = 1.38 x 10-23 J/K x 290 K = 4 x 10-21 W/Hz = -204 dBW/Hz The thermal noise in a bandwidth of B Hertz can be expressed as N = k x T x B in decibel: N = 10 log k + 10 log T + 10 log B = (-228.6 + 10 log T + 10 log B) dBW Example: Given a receiver with an effective noise temperature of 294 K and a 10 MHz bandwidth, the thermal noise level at the receiver’s output is N = (-228.6 + 10 log (294) + 10 log (107) ) dBW = (-228.6 + 24.7 + 70) dBW = -133.9 dBW