By Richard S. Prodan, Ph.D. , Majid Chelehmal, Ph.D., Tom Williams, CableLabs
This paper presents an analysis of the effects and potential sources of transient impairments found in field testing of two-way cable systems currently supporting trials of digital transmission equipment for two-way services. Data on the characteristics and statistics of impairments that have been captured over extended time periods using a device known as the CW Tester™ are presented. This device demodulates a test carrier wave into in-phase (I) and quadrature ( Q) baseband signals. When a transient impairment is sensed, the device triggers a digital oscilloscope to acquire the demodulated impairment. The impairment data is stored on a computer for subsequent analysis using a data browsing software analysis tool for detailed inspection of individual impairments, as well as for longer term statistical analysis and transmission performance characterization. The results of laboratory experiments designed to replicate and thus identify the source of some impairments are compared with similar characteristics observed in the field.