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Phenomenologicai explanations of the electrical characteristics of the polymer thick film resistors  are given. The conduction mechanism is discussed on the basis that the sheet resistivity is dependent on the average gap distance between carbon black conducting particles or chains. The effect of the "structure'! of carbon blacks has also been incorporated. The dependencies of sheet resistivity on both the content of carbon blacks and the structure of carbon blacks have been studied. The current noise indices (CNI) of the polymer thick film (PTF) resistors have been explained, qualitatively, by the same model. The relationships between sheet resistivity and the CNI, and the resistor geometries on the CNI have been examined with the aid of a model of noise generators. The temperature coefficient of resistance and the percentage variations of resistance was studied on the basis of the thermal motion (Brownian) of the Carbon black particles and the thermal expansion of the polymer resins. The improved electrical characteristics of the PTF resistors, prepared with the blended carbon blacks, were also studied.