technology has been used extensively by the broadcast and cable
television industries, as well as in other telecommunications applications,
since the early 1950s. Today, microwaves are employed by telecommunications
industries in the form of both terrestrial relays and satellite
are a form of electromagnetic radiation with frequencies ranging
from several hundred MHz to several hundred GHz and wavelengths
ranging from approximately 1 to 20 centimeters. Because of their
high frequencies, microwaves have the advantage of being able to
carry more information than ordinary radio waves and are capable
of being beamed directly from one point to another. In addition
to their telecommunications applications (which include telephony
and computer networking, as well as television), microwaves are
used in cooking, police radar, and certain military applications.
microwave is a "line-of-sight" technology (i.e., because a microwave
transmission cannot penetrate the earth's surface, it will not extend
beyond the horizon), long-distance terrestrial transmission of messages
is accomplished via a series of relay points known as "hops." Each
hop consists of a tower (often atop a mountain) with one antenna
(typically a parabolic antenna) for receiving and another for retransmitting.
Hops typically are spaced at 25-mile intervals.
Prior to the widespread use of communications satellites in television
industries, terrestrial microwave relays frequently were used to
deliver programming from broadcast networks to their affiliates,
or to deliver special event programming, such as sports, to local
stations. Beginning in the 1950s, terrestrial microwave relays were
employed to supplement expensive telephone land lines for long distance
transmission of programming.Microwave
mobile units (vans with microwave transmitters attached) have also
been used in television news reporting since the late 1950s.
technology was critical to the development of the community antenna
television (CATV) industry. Before microwave technology became available
in the early 1950s, local CATV systems were limited in channel selection
to those stations that could be received over-the-air via tall "master"
antennas. In such situations, a CATV system could flourish only
within 100-150 miles of the nearest broadcast television markets.
Microwave relays, however, made it possible for CATV systems to
operate many hundreds of miles from television stations. The new
technology thus was a boon to remote communities, especially in
the American West, which could not have had television otherwise.
also introduced the possibility for CATV operators to select which
broadcast signals they would carry, sometimes allowing them to bypass
closer signals in order to provide their customers with more desirable
programming--perhaps from well-funded stations in large cities.
For this reason, it was microwave technology above all that prompted
the earliest efforts by the Federal Communications Commission to
regulate CATV. By the late fifties, some concern had been voiced
by broadcasters as to the legality of the retransmission--and, in
effect, sale--of their signals by CATV systems and CATV-serving
microwave outfits. The most notable of these complaints resulted
in the Supreme Court case, Carter Mountain Transmission Co. v.
FCC (1962). In 1965 and 1966 respectively, the FCC issued two
bodies of regulation to govern the rapidly growing CATV industry.
Both of these focused primarily on the legalities of microwave-delivered
rules did very little to curtail the growth of CATV (more widely
known as "cable television" by the late 1960s), however, and microwave
continued to play a key role. Throughout the U.S., the signals of
several independent television stations, some of which have become
cable "superstations," were delivered to cable systems by microwave.
Also, in late 1972 and early 1973, Home Box Office began serving
customers in the Northeast via two existing microwave relay networks.
then, terrestrial microwave technology accomplished many of the
television programming tasks for which communication satellites
are used today. Terrestrial relays still exist and serve many important
functions for television. In recent years, they have also been enlisted
for non-television applications such as computer networking and
the relaying of long distance telephone messages. Some companies
that began as terrestrial microwave outfits have also diversified
into satellite program delivery.
Steven and Frederic H. Levien. Microwaves Made Simple. Dedham,
Massachusetts: Artech, 1985.
Operator's Handbook. Editors of BM/E Magazine. Blue Ridge Summit,
Pennsylvania: TAB Books, 1973.
Power Television; Translators;