Noise from Current-Carrying Resistors 20 to 500 Kc

Measurements have been made of the effect, first studied by Bernamont that when a direct current is flowing through certain types of resistors, the noise voltage generated at their terminals is considerably in excess of the thermal value. The effect has been investigated for solid carbon-composition, "metallized," palladium film, and "cracked-carbon" resistors, for resistance values from 1,000 to 30,000 Ω, currents from 1 to 10 milliamperes, and at frequencies between 20 and 500 kc. For some individual resistors, especially of the solid carbon-composition type, the noise voltage measured at any frequency in the range stated (with direct current flowing) showed much larger fluctuations than those characteristic of thermal noise, with a detecting system having a response up to a few cps. The fluctuations frequently reached peak amplitudes of several times the mean level of the noise. Several records of the fluctuations; taken on a recording meter, are shown. The fluctuations were particularly large when the current was first applied to any resistor, while its resistance changed to a stable value at a higher temperature, suggesting an analogy to the Barkhausen effect in the magnetization of ferromagnetics. No simple correlation of the occurrence of the fluctuations with other factors has been found.