Digital Equipment Corporation

Martin Minow

David Gerard Conroy

Edward A Bruckert

Richard D Ellison

The present system employs a high speed digital signal processor which is programmed to generate pairs of digitized waveforms, each pair representing a pair of different frequencies in response to coded input signals. Each pair of different digitized waveforms, when converted and combined into an analog signal, represents a 'tone pair' as used in major telephone systems. The tone pairs are transmitted through an anti-aliasing filter circuit and therefrom through amplification circuitry to a tone pair decoder of the type used in major telephone systems. At the tone pair decoder the tone pair signals are reconverted into binary signals. The binary signals from the tone pair decoder are transmitted to a data processor in the system under test, whereat they may or may not be further decoded. Ultimately the binary signals are compared with the coded input signals originally sent. In this way, the system which is designed to handle digital signals and which is designed to handle digital to analog conversions, is tested. The test circuit employs components already present in the system, or readily adaptable from the major telephone systems equipment.

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Arlington, MA, United States of America

Martin Minow