Technical Digests--Measurement of Telephone Noise and Power Wave Shape

N studies of the inductive coordination of power and telephone systems from the noise standpoint, a knowledge of the magnitudes of the harmonic currents and voltages on the power circuits and of the harmonic components of the telephone circuit noise is necessary. It is also necessary that there be available a means of rating and summing up these individual components to give an overall indication of their effects on a person using a telephone connected to one of the exposed circuits. This paper discusses methods which have been developed for making such overall measurements. The effect on a listener of a given amount of noise on a telephone circuit is a complex one, and it is not practicable in the day-by-day maintenance of telephone circuits to measure separately all the factors involved. Rather, it is necessary to make some overall measurement of the circuit noise which may be related to its effect on telephone transmission. It is, of course, desirable that the measuring devices used should measure different circuit noises as equal when they produce equal interfering effects on telephone transmission. Two methods of measuring telephone circuit noise are at present in use in the Bell System. One of these methods is subjective, that is, uses the human hearing mechanism as a part of the measuring apparatus. This method consists of comparing, in a telephone receiver, the noise to be measured with a noise generated by means of a standard buzzer. The observer adjusts the magnitude of the buzzer noise by means of a calibrated potentiometer until, in his judgment, it is as disturbing as the noise to be measured.