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T h ree
Cha p te r
FIGURE 3.63 Two active star couplers.
separated by some distance. The star coupler then becomes the dis-
tributor of the light signals to the racks in each cluster, as well as a
potential repeater to a star in another cluster.
3.18.4 Hybrid Fiber Networks
Star and daisy chain network structures can be combined to mini-
mize overall cabling costs (Fig. 3.64). The fiber network configuration
exactly duplicates the coax network. The final decision on exactly
which configuration to choose depends on the following criteria:
• Economical cabling layout
• Length of cable runs versus cost of electronics
• Location of end devices and power availability
• Power-out considerations
Other considerations specific to the programmable controller
being used can be summarized as follows:
• Pulse-width. Total acceptable pulse-width distortion, which
may limit the number of allowable repeater sites, is
Allowable distortion (ns) = allowable percent distortion
× period of signal (ns)
