A DSP IMPLEMENTATION OF A SUBSCRIBER LOOP TESTER
van Melle, Ehren Johannes Dirk
The subscriber loop forms the final link between the. subscriber and the actual telephone network. The pair of twisted copper wires which form the loop must be well maintained to avoid poor quality service to subscriber or customer. By conducting periodic testing of the subscriber loop, the telephone company can ensure the high standards of service that they desire. The purpose of this research project is to design a new loop tester based on a digital signal processing (DSP) chip, replacing the old analog-based testers. The DSP chip uses an analog-digital converter (ADC) to take sample measurements of various signals on the subscriber loop and a digital-analog converter (DAC) to output control signals. Various algorithms are first analyzed and tested to verify their results for the tests required. Next, these algorithms are added to the software running on the DSP chip. The algorithms are then tested versus known input values to qualify the testing procedure and analysis for use on an actual subscriber loop. Finally, the software is used to provide test results of various fault conditions on a pair of twisted copper wires. The results from these tests show that the DSP-based loop tester can measure varying line resistance and capacitance due to faults present on the subscriber loop, which can lead to accurate fault analysis.