the exchangeable power at the terminals of a one port device due solely to its sources of noise
NOTE 1 – A receiving antenna can be regarded as a one-port device when viewed from its output port.
NOTE 2 – If the impedance of the device has a constant real part at thermodynamic temperature T and if quantum effects are neglected, the exchangeable noise power spectral density due solely to thermal noise of the device is independent of frequency and equal to kT where k is Boltzmann's constant.
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