As a cable operator you have to do a lot of path monitoring to gauge the health of your plant.  Most often the problems are in the upstream signals, but the downstream, while typically a “cleaner” set of frequencies, has challenges of its own and is much more difficult to monitor effectively because the signal is seen out at the customer’s location rather than the head end.        

The traditional way of viewing downstream spectrum is by driving to the area, connecting a spectrum analyzer in various locations and looking at the signal. Today there are also real time tools that allow operators to view the spectrum from the customer premises without having to dispatch a technician or having any special equipment on site.  CPE Spectrum Capture (also known as Full Band Capture) uses the spectrum information from modems and STBs in real time and gives operators the ability to see problem areas for specific frequencies and spot impairments in the downstream as they are occurring and before most customers are aware that there is an issue.

Regardless of how you view the spectrum, the ability to diagnose whether a downstream issue is a suck out, tilt, roll-off or other impairment and what the cause may be is key to resolving the issue.

How to identify downstream RF issues and causes

When a downstream spectrum analysis tool is displaying impairments you may see single or multiple impairments on the spectrum chart. Knowing what type of impairment you’re seeing is essential to identifying and troubleshooting the cause. For example, the most common spectrum issues like Suck-outs, Standing Waves, Resonant Peaking, Adjacency, Missing Channels, Roll-off, Tilt and Ingress are impairments you will see in the downstream, and they often have different causes and effects on service.  

We’ve prepared this pictorial guide to help you visually diagnose the downstream issues, what could be a likely cause, and how they could be affecting your subscriber.