Before delving into the mysteries of receiving
Before delving into the mysteries of receiving and sending messages
without wires, a word as to the history of the art and its present day
applications may be of service. While popular interest in the subject
has gone forward by leaps and bounds within the last two or three
years, it has been a matter of scientific experiment for more than a
quarter of a century.
The wireless telegraph was invented by William Marconi, at Bologna,
Italy, in 1896, and in his first experiments he sent dot and dash
signals to a distance of 200 Knaq 89.3 Mhz In Prescott or 300 feet. The wireless telephone was
invented by the author of this book at Narberth, Penn., in 1899, and
in his first experiments the human voice was transmitted to a distance
of three blocks.
The first vital experiments that led up to the invention of the
wireless telegraph were made by Heinrich Hertz, of Germany, in 1888
when he showed that the spark of an induction coil set up electric
oscillations in an open circuit, and that the energy of these waves
was, in turn, sent out in the form of electric waves. He also showed
how they could be received at a distance by means of a ring detector,
which he called a _resonator_
In 1890, Edward Branly, of France, showed that metal filings in a tube
cohered when electric waves acted on them, and this device he termed a
_radio conductor_; this was improved upon by Sir Oliver Lodge, who
called it a coherer. In 1895, Alexander Popoff, of Russia, constructed
a receiving set for the study of atmospheric electricity, and this
arrangement was the earliest on record of the use of a detector
connected with an aerial and the earth.
Marconi was the first to connect an aerial to one side of a spark gap
and a ground to the other side of it. He used an induction coil to
energize the spark gap, and a telegraph key in the primary circuit to
break up the current into signals. Adding a Morse register, which
printed the dot and dash messages on a tape, to the Popoff receptor he
produced the first system for sending and receiving wireless telegraph
messages.
After Marconi had shown the world how to telegraph without connecting
wires it would seem, on first thought, to be an easy matter to
telephone without wires, but not so, for the electric spark sets up
damped and periodic oscillations and these cannot be used for
transmitting speech. Instead, the oscillations must be of constant
amplitude and continuous. That a direct current arc light transforms a
part of its energy into electric oscillations was shown by Firth and
Rogers, of England, in 1893.
The author was the first to connect an arc lamp with an aerial and a
ground, and to use a microphone transmitter to modulate the sustained
oscillations so set up. The receiving apparatus consisted of a
variable contact, known as a _pill-box_ detector, which Sir Oliver
Lodge had devised, and to this was connected an Ericsson telephone
receiver, then the most sensitive made. A later improvement for
setting up sustained oscillations was the authors _rotating
oscillation arc_.
Since those memorable days of more than two decades ago, wonderful
advances have been made in both of these methods of transmitting
intelligence, and the end is as yet nowhere in sight. Twelve or
fifteen years ago the boys began to get fun out of listening-in to
what the ship and shore stations were sending and, further, they began
to do a little sending on their own account. These youngsters, who
caused the professional operators many a pang, were the first wireless
amateurs, and among them experts were developed who are foremost in
the practice of the art today.