Mark K Lewandowski

US Patent:

48706752, Sep 26, 1989

Filed:

Nov 28, 1988

Appl. No.:

7/276742

Inventors:

Richard C. Fuller - Fair Haven NJ
Thomas A. Gentles - Freehold NJ
Mark Lewandowski - Aberdeen NJ

Assignee:

American Telephone and Telegraph Company - New York NY
AT&T Information Systems Inc. - Morristown NJ

International Classification:

H04M 124
H04M 326
H04B 346

US Classification:

379 5

Abstract:

Currently, metallic loops are tested for shorts, opens and grounds by applying a test signal (DC or 20 Hz) directly to the metallic looop. A test signal cannot be applied to any part of the network other than the metallic loop because it will be blocked by the A-to-D converters and the hybrid of the system before it can reach the metallic loop. In this invention, digital signal processing is used to test a metallic loop for shorts, opens, grounds and the presence of loading coils from a remote location. Direct metallic connection to the metallic loop is no longer necessary. Briefly, a test signal, in digital form, is fed into the network at some convenient location remote from the metallic loop that is to be tested. As the signal passes through the A-to-D converter from the digital section of the network to the analog metallic loop, it is converted by the A-to-D converter into an analog signal having a specific frequency and a predetermined amplitude. Defects - opens, shorts and grounds - in the metallic loop cause reflections of the analog test signal.