An Evaluation of Two Simple Methods for Detecting Tones over Telephone Lines

The need to reliably detect tones arises in a number of systems which are in use within the telephone plant. A wide variety of methods have been proposed for solving this problem including digital filtering, spectral analysis etc. 1 " 1 In this paper we discuss a particular problem in tone detection and show some characteristics of two simple systems designed to solve this problem. Figure 1 shows a pictorial description of a simple telephone call in which the calling party initiates a call and the call is switched through a central office. When the called party picks up the telephone a dc path 1513 Fig. 1--Pictorial description of a simple telephone call.