City of Light: The Story of Fiber Optics

A VISION OF THE FUTURE 83
Point Laboratory in 1925, he built a 20-megahertz (million-cycle) transmitter
emitting ‘‘short waves’’ 15 meters (50 feet) long. Not only did the signals
reach South America in daytime, but the short waves did not require the
gigantic antennas needed for long waves, so the short-wave transmitter cost
a mere $15,000, compared to $1.5 million for a long-wave transmitter that
didn’t work as well. 16 International broadcasters and amateur radio operators
still transmit short-wave signals around the world. Higher frequencies followed
as electronic circuits improved, and radio broadcasts claimed chunks
of the spectrum.
As electronic circuits improved, telephone engineers learned how to multiplex
many voices, using each one to modulate a different frequency, and
sending them all through the same wires. Multiplexed 24-phone channels
require 24 times the bandwidth of a standard phone line, but it’s much
cheaper than stringing 24 separate pairs of wires. Further improvements in
electronics allowed multiplexing hundreds of telephone channels. National
telecommunications networks spread around the world, often carrying the
voices for radio networks as well as telephones.
Increasing demand, and prospects for future television systems, pushed
engineers to ever higher frequencies. Above about 10 megahertz, the only
reliable radio transmission is in the line of sight, so Hansell’s team at Rocky
Point developed chains of radio towers to relay experimental television signals.
They started at 80 megahertz and by 1939 had reached 500 megahertz. 17
Although they built the system for television experiments, the same equipment
could carry radio and telephone signals.
Radio frequencies passed a billion hertz (a gigahertz) with the development
of microwave radar during World War II. However, ordinary vacuum tubes
were not fast enough to amplify gigahertz signals. Reaching those frequencies
required complex new tubes, called klystrons, magnetrons, and travelingwave
tubes, that were much bulkier and costlier than ordinary thumb-sized
vacuum tubes.
The continued spread of telephones and the advent of commercial television
broadcasting put new demands on the postwar communications network.
After the war, chains of microwave relay towers operating at a few
gigahertz (billion hertz) sprouted across Europe and America. They were the
biggest information pipelines money could buy in the 1950s, but the towers
could be no more than about 50 miles (80 kilometers) apart or the Earth’s
curvature would block the microwave beam.
To bridge the Atlantic, an international consortium of public and private
telephone companies turned to coaxial cable, a copper wire separated from a
metal sheath by a plastic insulator, like modern television cables. Submarine
telegraph cables had been in service across the Atlantic since the 1860s, but
they did not need amplifiers. Telephone cables did, and only in the 1950s
were electronic amplifiers up to the job of working on the ocean floor for the
25-year period needed to make the cables economical to operate. The consortium
spent $37 million on undersea equipment to replace radio telephones
dating from the 1920s and 1930s. AT&T supplied the cable from Scotland to