Audio-frequency constants of circuits and telephone lines

Bridge methods of measurement of circuit constants at higher audible and carrier frequencies require expensive apparatus and skilful manipulation, and become difficult at higher frequencies. Prof. E. Mallett developed simpler methods to determine the resonant frequency and decay-factor of electro-mechanical vibrators, and deduced their dynamical constants. The methods were applied by Prof. Mallett and Mr. Blumleinf to find the high-frequency resistance of coils, circuits, etc. The present paper extends the application to determine the primary constants of telephone and other circuits at higher audible and carrier frequencies. Measurements were confined to the frequency band 3 to 12 kilocycles per sec. The resonant frequency and decay factor of telephone and other circuits were determined from (Z/Zd)¿ f curves and derived vector diagrams (which were circles). The values of R, L, and G, of the circuits at 6-53 kilocycles per sec. were deduced. In the case of an overhead telephone loop, R and L were found at 6-575 and C at 11-03 kilocycles per sec. A circuit capacitance variation of the order of 0.0005 ¿F could be easily determined by the application of the methods at 6.6 kilocycles per sec.