By John Chrostowski, Benny Lewandowski & Dan Rice, Comcast; Greg Tresness, Arcom Digital, LLC.
System leakage monitoring is an integral and extremely important aspect of system maintenance. Federal Communications Commission (FCC) leakage requirements, test and mitigation methods for present cable systems with 5-42 MHz and 5-85 MHz return bands are well understood. Leakage signal sources, monitoring equipment, methods and measurement programs are all in place for measurements in the downstream band, 54-1000 MHz, with an emphasis on the aeronautical band of 108-137 MHz. The FCC sets maximum individual signal leakage levels for cable systems, with more stringent limits on cable systems that may interfere with aeronautical and navigation communications.
In a traditional cable system with a 5-42 MHz return band, high level signals in the downstream are present at the headend or node output, and at the home, the downstream signal is at its lowest level. What happens if you increase the upper boundary of the upstream signal path to 204 MHz or higher? The system is essentially turned upside down, with the highest signal levels in the aeronautical band (108-137MHz) at the home, and the lowest upstream signal levels at the headend or node.
This paper will look at the implications of these inverted plant levels. How do the FCC’s cable signal leakage requirements apply to this scenario? Can the same leakage tools and methods be used? What changes and considerations need to be made? These questions not only apply to high split plants with 204 MHz upstream, but also to future full duplex data over cable service interface specification.
(FDX DOCSIS) and extended spectrum DOCSIS (ESD) systems, each with upstream signals well beyond 204 MHz.
This paper will review these considerations and discuss the implications of the “inverted” plant. Different options and scenarios will be examined, and their implementation and feasibility evaluated to help readers ensure a solid leakage measurement program is in place for when these plant upgrades are implemented.