SCTE 280 2022

Understanding and Troubleshooting Cable RF Spectrum

Executive Summary

The DOCSIS® 3.0 specification introduced a feature known as full band capture (FBC), enabling cable modems to report radio frequency (RF) spectrum data. This creates an unprecedented opportunity to observe RF performance in ways that were previously impossible. Most operators now have access to spectrum analysis functionality at nearly every location where FBC-capable DOCSIS customer premise equipment (CPE) have been installed. While there is plenty of material available that explains spectrum analysis, SCTE’s Network Operations Subcommittee Working Group 7 (NOS WG7) members have discovered and cataloged many cable-specific nuances and have compiled a significant amount of material on this topic.

This Industry Reference (IR) discusses the fundamentals of cable RF, impedance, resolution bandwidth, return loss, noise, velocity of propagation (VoP), and other parameters. An understanding of these topics is especially useful when examining different cable environments and architectures. This Industry Reference also covers the differences in spectrum analysis tools such as FBC vs. traditional frequency-swept spectrum analyzers. Finally, it provides an in-depth analysis and means to identify many common cable impairments (including examples). Among the examples are problems such as damaged coaxial cables, loose connectors, faulty amplifiers, water-soaked drops, bad or missing terminations, and more. The goal of this document is to help cable operators, especially technicians, be successful in finding and fixing cable plant failures that disrupt RF transmission, thus impacting service.


The material contained within this document applies directly to DOCSIS 3.0 and higher compliant CPE which have implemented full band capture functionality. It does not include non-DOCSIS connected devices such as MoCA or Wi-Fi, which may have similar but different capabilities.


This Operational Practice provides a valuable tool to cable field operations and engineers to better interpret cable RF spectrum performance. The document also provides operational perspectives about detecting, interpreting, and repairing problems that are often unique to coaxial cable networks. The intent of this document is to produce consistent interpretation and treatment of problems, improve repair times, and reduce rework caused by misinterpretation.

Intended Audience

The intended audience of this document is primarily field-facing technicians, but the document is also useful for analysis and repair teams. It also may be useful for software designers and systems engineers.