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Troubleshooting Noise Part Two

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Troubleshooting Noise, 860DSPi

Troubleshooting Noise /Part Two

 

In the last article about Troubleshooting Noise we went over tracking noise and how it affected the return path. The return path is where we generally have our Modems Upstream channels, Box Guide and Hits Data streams and VOD requests. We would do well to take care of all of these by keeping this return path clean and free of any noise greater then -30. In our example we talked briefly about a service call a customer had that various techs had been to but couldnt find the issue. The issue was noise in the return band which was so bad it affected VOD requests. We also barely touched on the small noise spikes in the Forward path that were most likely affecting Digital Video Services. We can cover that now.

Recently there was a job referred to a local maintenance dept. The technician arrived on site for Digital Tiling. He performed all of his tests, Home Cert, Spectrum Check, various QAMs and of course spending time on the channels he was having issues with. He found the affected channels MER to be at 29-30 and BER to hover around 5.00-E-06. This would definitely cause tiling. The tech also noted that it was only on a handful of PODs, or Channels. Everything around these channels were in spec, no issues.

I will skip the details of the troubleshooting that brought the line tech to the actual issue as it is repeating another article you can find by clicking this text. I will say this however, the issue was caused by a Direct TV customer who had fed their Direct TV feed into the homes cabling and also back out to the cable plant. What this did was inject a pretty serious carrier back into the cable plant that caused all kinds of impairments on the QAM channels that were occupying the same spectrum.

In simpler terms, We have a digital carrier on say 549MHz. This carrier holds compressed and encrypted channels like HBO, TLC and we will say ESPN. If another carrier is injected into the plant on this same frequency, or through this frequency it will severely “screw up” the channel we are putting out. This is keeping our plant clean. This is ensuring that cable stays a “closed loop system”. Nothing gets in to interrupt our signal carriage and nothing gets out to affect other services.

Troubleshooting Ingress, 860DPSi Spectrum Test, Cabletechs.orgThe screenshot is the actual carrier. This is a rather large carrier and it occupied the space of about 10 cable PODs which all in all wiped out 50 or so channels. Once the drop was disconnected from the Direct TV sub, the MER popped up to 38, BER was solid at 1.00-E-09 and services were restored. I will try to get a screenshot of our same spectrum and our carriers for the purpose of this example and append them to this article.

This article is less of a “troubleshooting” article and more of a “look out for this” article. Taking care of our spectrum and keeping it clean is every techs jobs. Make sure we are shooting our drops and homes for ingress at every job. Doing our best to keep the plant clean and our customers homes as well.

Keep a look out for another article on how to set up your 860DSPi for accurate viewing of the return and forward spectrum!

The post Troubleshooting Noise Part Two appeared first on cT.o.


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