| the exchangeable noise power spectral density at a given frequency of a one port device divided by Boltzmann's constant
NOTE 1 – This definition assumes that quantum effects are negligible.
NOTE 2 – The spot noise temperature has the sign of the real part of the device impedance.
NOTE 3 – If the device has an impedance with a positive real part, its noise temperature at a given frequency equals the thermodynamic temperature to which a resistor equal in value to the real part of the impedance should be brought in order to obtain an available power of thermal noise equal to the available power of noise of the device at the same frequency.
NOTE 4 – A receiving antenna can be regarded as a one-port device when viewed from its output port.