Time Variations and Harmonic Content of Inductive Interference in Urban/Suburban and Residential/Rural Telephone Plants

The time variations and harmonic content of longitudinal (common-mode) interference present on a wide variety of telephone lines in both urban/suburban and residential/rural environments have been measured. Significant levels of 60 Hz and its next 15 odd-harmonics were present. Variations with time ranged from an insignificant amount to over 20 dB. Interference trends relative to the size of the central office (CO), i.e., number of lines, were noted. In addition to showing noise trends with time, the results indicated desirable periods to record average noise conditions, times to record peak noise, and the important harmonics to measure. Such data are helpful to telephone company engineers in their cooperative efforts with power companies to isolate and correct interference problems. This coordination should result in greater compatibility between the operations of the two utilities. These data will also aid telephone designers to design equipment that will reduce the adverse noise effects of the telephone operating environment.