Abstract :
THE PRESENCE of harmonics in an a-c circuit, inductively coupled to a telephone system, may cause interference with the transmission of sound. As the result of a series of tests, a meter to measure Telephone Influence Factor (TIF), commonly called a TIF meter, was developed. The admittance characteristic of this meter, for various frequencies, is proportional to the values in the curve and tabulation in Figure 1. Quantitatively, TIF for any frequency, or combination of frequencies, is equal to the microamperes per volt input, as measured by this meter. TIF for 60 cycles is 1. As will be noticed from the curve, a frequency of 1,070 cycles has 12,000 times the interfering effect of a 60-cycle fundamental of the same amplitude. By use of a harmonic analyzer, the contribution of each component to the total TIF may be determined.
