Long-distance radiotelephony

The invention: The first radio transmissions fromthe United States
to Europe opened a new era in telecommunications.
The people behind the invention:
Guglielmo Marconi (1874-1937), Italian inventor of transatlantic
telegraphy
Reginald Aubrey Fessenden (1866-1932), an American radio
engineer
Lee de Forest (1873-1961), an American inventor
Harold D. Arnold (1883-1933), an American physicist
John J. Carty (1861-1932), an American electrical engineer
An Accidental Broadcast
The idea of commercial transatlantic communication was first
conceived by Italian physicist and inventor Guglielmo Marconi, the
pioneer of wireless telegraphy. Marconi used a spark transmitter to
generate radio waves that were interrupted, or modulated, to form
the dots and dashes of Morse code. The rapid generation of sparks
created an electromagnetic disturbance that sent radio waves of different
frequencies into the air—a broad, noisy transmission that was
difficult to tune and detect.
The inventor Reginald Aubrey Fessenden produced an alternative
method that became the basis of radio technology in the twentieth
century. His continuous radio waves kept to one frequency,
making them much easier to detect at long distances. Furthermore,
the continuous waves could be modulated by an audio signal, making
it possible to transmit the sound of speech.
Fessenden used an alternator to generate electromagnetic waves
at the high frequencies required in radio transmission. It was specially
constructed at the laboratories of the General Electric Company.
The machine was shipped to Brant Rock, Massachusetts, in
1906 for testing. Radio messages were sent to a boat cruising offshore,
and the feasibility of radiotelephony was thus demonstrated.
Fessenden followed this success with a broadcast of messages and music between Brant Rock and a receiving station constructed at
Plymouth, Massachusetts.
The equipment installed at Brant Rock had a range of about 160
kilometers. The transmission distance was determined by the strength
of the electric power delivered by the alternator, which was measured
in watts. Fessenden’s alternator was rated at 500 watts, but it
usually delivered much less power.
Yet this was sufficient to send a radio message across the Atlantic.
Fessenden had built a receiving station at Machrihanish, Scotland,
to test the operation of a large rotary spark transmitter that he
had constructed. An operator at this station picked up the voice of
an engineer at Brant Rock who was sending instructions to Plymouth.
Thus, the first radiotelephone message had been sent across
the Atlantic by accident. Fessenden, however, decided not to make
this startling development public. The station at Machrihanish was
destroyed in a storm, making it impossible to carry out further tests.
The successful transmission undoubtedly had been the result of exceptionally
clear atmospheric conditions that might never again favor
the inventor.
One of the parties following the development of the experiments
in radio telephony was the American Telephone and Telegraph
(AT&T) Company. Fessenden entered into negotiations to sell his
system to the telephone company, but, because of the financial panic
of 1907, the sale was never made.
Virginia to Paris and Hawaii
The English physicist John Ambrose Fleming had invented a twoelement
(diode) vacuum tube in 1904 that could be used to generate
and detect radio waves. Two years later, the American inventor Lee
de Forest added a third element to the diode to produce his “audion”
(triode), which was a more sensitive detector. John J. Carty, head of a
research and development effort at AT&T, examined these new devices
carefully. He became convinced that an electronic amplifier, incorporating
the triode into its design, could be used to increase the
strength of telephone signals and to long distances.
On Carty’s advice, AT&T purchased the rights to de Forest’s
audion. A team of about twenty-five researchers, under the leadership of physicist Harold D. Arnold, were assigned the job of perfecting
the triode and turning it into a reliable amplifier. The improved
triode was responsible for the success of transcontinental cable telephone
service, which was introduced in January, 1915. The triode
was also the basis of AT&T’s foray into radio telephony.
Carty’s research plan called for a system with three components:
an oscillator to generate the radio waves, a modulator to add the
audio signals to the waves, and an amplifier to transmit the radio
waves. The total power output of the system was 7,500 watts,
enough to send the radio waves over thousands of kilometers.The apparatus was installed in the U.S. Navy’s radio tower in
Arlington, Virginia, in 1915. Radio messages from Arlington were
picked up at a receiving station in California, a distance of 4,000 kilometers,
then at a station in Pearl Harbor, Hawaii, which was 7,200
kilometers from Arlington. AT&T’s engineers had succeeded in
joining the company telephone lines with the radio transmitter at
Arlington; therefore, the president of AT&T, Theodore Vail, could
pick up his telephone and talk directly with someone in California.
The next experiment was to send a radio message fromArlington
to a receiving station set up in the Eiffel Tower in Paris. After several
unsuccessful attempts, the telephone engineers in the Eiffel Tower
finally heard Arlington’s messages on October 21, 1915. The AT&T
receiving station in Hawaii also picked up the messages. The two receiving
stations had to send their reply by telegraph to the United
States because both stations were set up to receive only. Two-way
radio communication was still years in the future.
Impact
The announcement that messages had been received in Paris was
front-page news and brought about an outburst of national pride in
the United States. The demonstration of transatlantic radio telephony
was more important as publicity for AT&T than as a scientific
advance. All the credit went to AT&T and to Carty’s laboratory.
Both Fessenden and de Forest attempted to draw attention to their
contributions to long-distance radio telephony, but to no avail. The
Arlington-to-Paris transmission was a triumph for corporate public
relations and corporate research.
The development of the triode had been achieved with large
teams of highly trained scientists—in contrast to the small-scale efforts
of Fessenden and de Forest, who had little formal scientific
training. Carty’s laboratory was an example of the new type of industrial
research that was to dominate the twentieth century. The
golden days of the lone inventor, in the mold of Thomas Edison or
Alexander Graham Bell, were gone.
In the years that followed the first transatlantic radio telephone
messages, little was done by AT&T to advance the technology or to
develop a commercial service. The equipment used in the 1915 demonstration was more a makeshift laboratory apparatus than a prototype
for a new radio technology. The messages sent were short and
faint. There was a great gulf between hearing “hello” and “goodbye”
amid the static. The many predictions of a direct telephone
connection between New York and other major cities overseas were
premature. It was not until 1927 that a transatlantic radio circuit was
opened for public use. By that time, a new technological direction
had been taken, and the method used in 1915 had been superseded
by shortwave radio communication.