How Cable Television Works

Cable television delivers a wide range of channels to your home using a sophisticated network of cables and signals. Initially, cable systems used microwave towers to capture distant broadcast signals, expanding viewing options for those outside the range of standard broadcasts. This marked the beginning of cable’s role in enriching television experiences.

The introduction of Community Antenna Television (CATV) led to the inclusion of a switch on television sets, allowing users to choose between standard broadcast frequencies allocated by the Federal Communications Commission (FCC) and the frequency plan used by cable systems. These two plans differed significantly in how they allocated the radio spectrum to various channels. Each television station received a 6-megahertz (MHz) slice of the radio spectrum. The FCC initially allocated portions of the Very High Frequency (VHF) spectrum to 12 television channels, dividing them into two groups to avoid interference with existing radio services.

With the increasing demand for television, the FCC allocated frequencies in the Ultra-High Frequency (UHF) spectrum, establishing channels 14 to 69 within the 470 MHz to 812 MHz range. Cable systems, utilizing coaxial cables instead of antennas, could use the “mid-band” frequencies (skipped by broadcast TV due to potential interference) for channels 14-22. The “CATV/Antenna” switch on the TV directed the tuner to either navigate around the mid-band (for broadcast) or tune directly through it (for cable).

Cable systems avoid using the same frequencies as broadcast channels 1 to 6 to prevent interference. Although cable equipment and televisions are designed to minimize interference, it can still occur, especially at connection points. When interference originates from the same channel carried on the cable, a problem arises due to the difference in signal transmission speed.

Radio signals travel through the air at nearly the speed of light, while in coaxial cables, they travel at approximately two-thirds the speed of light. This difference in speed can cause a slight delay between broadcast and cable signals reaching the TV tuner, resulting in a double image known as “ghosting.”

In 1972, the first pay-per-view channel, Home Box Office (HBO), emerged, offering individual movies and sporting events for a fee. Initially a regional service, HBO expanded nationally in 1975 by transmitting its signal to a satellite in geosynchronous orbit and then down to cable systems across the country. Early satellites could handle up to 24 channels, requiring cable systems to use multiple large dish antennas, one for each channel. This marked the establishment of the modern cable system architecture.

With the growth of programming options, cable system bandwidth increased from 200 MHz (supporting 33 channels) to 550 MHz and beyond, accommodating over 91 channels. Further advancements like fiber optics and analog-to-digital conversion enhanced broadcast quality and channel capacity significantly.