Abstract: A cable tester, which is adapted to be used by persons not expertly skilled in the technical characteristics of local area networks (LANs), is disclosed. The tester incorporates a time domain reflectometer which starts a counter upon the generation of an incident signal pulse and utilizes a comparator which compares signals present on a cable under test to a controllable amplitude to halt the timer. The tester exhibits an output impedance which is greater than the impedance of a cable being tested. The tester additionally measures instantaneous amplitude levels of signals present on the cable being tested, resistance, continuity, noise levels, and data activity on a network of which the cable is a part. In addition, the tester includes a display and a sound generally device. Software programming compensates for impedance mismatches with the cable and data present on an active network being tested.