5-3
F i b e r
Fig. 5-2 Customers Affected by 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 more and more varied
transmitters of RF energy 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) that are at known locations (where better care can be taken
with shielding), there are lots of transmitters that can be right next to
the network and are not controlled.
Random Noise- Noise can be generated by non-transmitters too.
Electric motor switching, welding, computers, or 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 or noise.