These were the predecessors to what we know today as cable television.  A cable system is made of the following basic components:  a headend and a tree-and-branch pattern.  At the headend, there is different equipment which handles the processing of incoming signals.  This equipment feeds the information into a modulator which readies it for transmission by assigning information from various source to their respective channels.  The headend compiles programs from numerous sources and sends them to homes through coaxial cable.  The tree-and-branch pattern branches off into feeder cables which bring signals into the neighborhoods of subscribers.  Then, cables referred to asdrop cables feed information into households that subscribe to the cable dealer.
    Cable uses radio energy to transmit signals enclosed in coaxial cable.  Radio energies are preserved while cable signals are sent through the coaxial cable.  Therefore, there is no need for antennas on homes.  Also, interference between channels is eliminated.
    Coaxial cable consists of two conductors and a hollow metal tube.  However, newer fiber optic cables are coming into use.  Fiber optic cables contain strands of pure glass about the size of a human hair.  One glass strand can hold more than 600 times as much information as coaxial cable.  Lasers (also called light-emitting diodes) generate beams of light which are carried in the fiber optic cables.  Fiber optic cable eliminated some of the attenuation associated with cable transmission.  Also, the cables are smaller.
    As with most technology, there are several drawbacks to cable.  First of all, the systems are costly to build and repair.  Second of all, a physical system has to be built.  Cable has to be buried in tunnels in order for transmission to be possible.   With broadcast, signals travel on invisible waves.
    There are also advantages to cable.  Cable uses VHF channels outside of the VHF part of the electromagnetic spectrum used for broadcasting.  This wider band gives viewers more selection, usually ranging from a minimum of 30 channels up to 100 channels.
Last Updated: May 19, 1999
Created by Diana Waxman , Jessica Bureau &Greg Roeberg