By Edward J. Callahan and Donald M. Bishop, Anixter Technologies (ANTEC)
Currently, increasing numbers of cable operators are adopting fiber optic distribution systems using AM-VSB modulated signals. While this technology has been shown to be cost effective in various hybrid fiber/coax architectures, the sizable deployment now taking place represents significant capital expenditures. As a result, operators are embarking on perhaps the most intensive product evaluations and cost/performance trade-off reviews in the industry's history. However, there are several sources of measurement anomalies that must be taken into account to obtain meaningful and reproducible results as these systems are moved from the Jab environment to the field.
This paper will focus on several sources of these anomalies such as spectrum analyzer frequency response, external bandpass filter tuning, software design utilized in automated testing, impedance matching of the system under test, etc. Also, several accuracy improvement techniques will be considered.