Cable TV Systems Illustrated - pág.3

intervals in cable systems to restore the original signal levels. Although
amplifiers boost the signal levels, each amplifier adds signal distortion (electrical noise). Due to the cumulative effects of amplification noise, the use of
amplifiers limits the maximum distance of a cable television distribution
system. Amplifiers may be installed approximately every 1,000 feet [2].

In the 1950s, cable system operators began experimenting with the insertion of other television programs that were not available in their local areas.
This allowed cable systems to offer programming that was unavailable via
normal television broadcast. This increased the interest of customers in purchasing cable television services.

Each analog television channel uses 6 to 8 megahertz (MHz) of the radio
spectrum to transfer both video signal (a majority of the bandwidth) and
audio. In the United States, the Federal Communications Commission
(FCC) initially allocated a frequency range within the very high frequency
(VHF) radio spectrum (below 300 MHz) to allow the transmission of up to 12
television channels. To provide additional television channels, the FCC allocated additional frequencies in the ultrahigh frequency (UHF) portion of the
radio spectrum (above 300 MHz). Channels 14 to 83 were created in the frequency range of 470 MHz to 894 MHz. The frequency bands for television
channels 70 through 83 were eventually reallocated (reassigned) for mobile
telephone services in the 1980s.

The first «pay-per-view» (PPV) channel was offered by a cable television system in Wilkes-Barre Pennsylvania in 1972 [²]. This was a regional service
called home box office (HBO). In 1975, HBO began transmitting nationwide
using satellite transmission. Early satellite systems could broadcast up to
24 channels for each satellite transponder. These early systems required the
use of relatively large dish antennas 10 meters in diameter and each channel required a separate antenna.