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On this day in engineering history, Guglielmo Marconi
announced that he had received the first transatlantic radio signal during
three days of wireless experiments. On December 12, 1901, the Italian inventor
claimed that his wireless telegraphy facility in St. John's,
Newfoundland (now part of Canada) had received faint but repeated signals
from a high-power, spark-transmitter station at Poldu, Cornwall, England.
The transmissions, which repeated the Morse code for the letter "S", convinced Guglielmo
Marconi that transatlantic wireless communications were possible – and
potentially profitable. Critics, however, disputed the inventor's claim because
Marconi failed to provide independent confirmation of the reported reception.
On December 11, 1901, Guglielmo Marconi watched as workers
raised an antenna supported by a kite and balloons high over Signal Hill in St. John's, Newfoundland (top left).
Meanwhile, across the Atlantic and 2100 miles away, associates in Poldu, Cornwall, England
readied a new spark-transmitter station which, unlike its battery-powered
predecessors, used a 35-kW alternator. Designed by J.A. Fleming, the inventor
of the vacuum tube rectifier, the transmitter consisted of a two-stage circuit.
The transmitting antenna was a fan with 54 vertical wires which were joined at
their lower ends and connected to the transmitter's feed line. The top of this
fan was approximately 200-ft. wide and suspended about 160 feet above the
ground.
In earlier experiments, Marconi's Poldu facility had
transmitted radio signals as far as several hundred miles. Encouraged by these
results, the Italian inventor now instructed his associates to transmit Morse
code for reception 2100 miles away in Newfoundland.
Between 11:30 AM and 2:30 PM St.
John's time, the Poldu facility transmitted messages
at 820 kHz with five-minute breaks. As historian Henry M. Bradford explains,
however, "Marconi could hardly have picked a worse combination of frequency and
time of day for the transatlantic experiment". During the day, the D-layer of
the ionosphere absorbs much of the energy from radio waves in this frequency
band. As listeners of AM radio stations can attest, long-distance reception is
better at night.
So did Guglielmo Marconi receive the first transatlantic
radio signal in December of 1901? Although Henry Bradford claims that
"descriptions of the receiving equipment used are sketchy", he speculates that
Marconi did not receive a radio signal on the first day of testing (December 11),
when accounts indicate that a tuned receiver was used. Nevertheless, Bradford does believe that Marconi heard something on
December 12, 1901 – but not at 820 Hz. "Spark
transmitters were notorious for the broadband emissions", the historian
explains, "and it is quite possible that the spectrum of the Poldu transmitter
contained significant power in the HF (short wave) band."
Resources:
http://www.antiquewireless.org/otb/marconi1901.htm
http://www.antiquewireless.org/otb/marconi1901a.htm
http://www.sparkmuseum.com/BOOK_FLEMING.HTM
http://en.wikipedia.org/wiki/Guglielmo_Marconi
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