Reverse Path Troubleshooting: Problems in Advanced Services
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Fig. 5-2 Customers Affected by a Return Path Ingress
Source
To see how this affects noise floors, think about how much of the network
can inject noise that affects a given customer. For forward path signals,
the only potential problem areas are the direct path from the customer’s
home to the headend. For reverse path signals, problems can come from
anywhere in the area served by one headend receiver.
• Many Diverse Ingress Sources: There are an increasing and varied
number of RF energy transmitters in the reverse path bands. CB radio,
short-wave, ham, paging, and land mobile all use the same frequencies
as a cable reverse path. Rather than a few transmitters (even at high
power) at known locations (where better care can be taken with
shielding), there are lots of transmitters that can be right next to the
network that are not controlled.
• Random Noise: Noise can be generated by non-transmitters too.
Electric motor switching, welding, computers, even power supply
switching can have energy in the reverse path band.
• Physical Plant Problems: Small cracks in powered coax or dissimilar
metal "diodes" can create CPD (common path distortion) or noise.
Fiber
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