Prequalification and Maintenance of DOCSIS 4.0 and DAA Cable Plants
A Pullout occurs when a hardline coaxial cable contracts longitudinally, usually in colder weather, and it can eventually be pulled out of its housing. This can lead to the separation of the shield or even the center conductor.
Pullouts will yield an adverse frequency response, especially at lower frequencies as shown in these Spectrum Analyzer measurement examples:
Below is how an active sweep depicts a pullout fault. Note the original sweep shown in orange, that shows an adverse slope in the low end, which would alert the user. The yellow trace shows a clean sweep after the pullout is repaired.
Suckouts are caused by mechanical or grounding issues in seizure screws, connectors, housing lids, or fittings. A suckout typically creates a severe ‘notch’ effect in the frequency response and can appear in both the Forward Path and Return Path. Below is how an active sweep depicts suckouts. Note the original Return Path sweep trace shown in orange, that shows a distinct notch. The yellow trace shows the clean sweep after the cause of the suckout is repaired.
Standing Waves are caused by a reflection due to an impedance mismatch somewhere in the plant. Typical causes are damaged cable or a crushed pedestal. Note the distinctive pattern of a standing wave, shown below in the original sweep, shown in orange. And the relatively smooth sweep, shown in yellow, after the impairment has been fixed.
Legacy Components. For DOCSIS 4.0 Spectrum Expansion, legacy components embedded in the plant must be identified and replaced, as they will kill signal transmission at extended frequencies. This appears as a severe roll-off. The Forward Path sweep trace below, shown in orange, reveals a roll-off, well within the applicable spectrum. The cause is a legacy passive device present in the system. The yellow trace shows the resultant sweep after the passive device is removed.
