A sampling wattmeter for noise power measurements

Low-frequency noise measurements are usually performed by measuring the voltage across a dipole, or the current through a wire. Here we demonstrate the feasibility of the measurement of the noise power flowing through a line connecting two dipoles. A sampling wattmeter. with spectral display capabilities, having a bandwidth in the range 1 Hz - 10 kHz and sensitivity better than 10(-22) W/Hz is here described, and employed to measure the noise power flowing between two resistors at different temperatures. Possible applications of the device include noise thermometry, noise measurement of active devices under load condition, investigations of excess noise below thermal threshold.