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. When the real part is positive, the exchangeable power becomes the available power.

NOTE 3 – If the device has an impedance with a positive real part, its spot 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 noise power of the device at the same frequency.

NOTE 4 – A receiving antenna can be regarded as one-port device when viewed from its output port.