The Dawn of Amateur Radio in the U.K. and Greece: A Personal ViewJoly, Norman F.
History
The Dawn of Amateur Radio in the U.K. and Greece: A Personal View
Joly, Norman F.
Radio broadcasting
The world's first patent for wireless telegraphy was awarded to
Marconi on the 2nd June 1896. In it he stated that "electrical action
can be transmitted through the earth, air or water, by means of
oscillations of high frequency." In the first public demonstration of
his equipment Marconi spanned the 365 metres between the G.P.O. and
Victoria street. Later, on Salisbury Plain, in March 1897, his
signals were detected over 7 kilometres away. On the 11th & 18th May
1897 messages were first exchanged over water. On the 27th of March
1899, during naval manoeuvres, Marconi bridged the English Channel for
the first time, a distance of about 140 kilometres. His transatlantic
triumph came on the 12th December 1901 when the morse letter 'S' was
transmitted from Poldhu, in Cornwall and received by Marconi himself
at St. John's, Newfoundland, who recorded the historic event in his
pocket book simply "Sigs at 12.20, 1.10 & 2.20".
The operation of Marconi's transmitter was itself quite
spectacular. To produce the oscillations he employed the oscillator
designed by Augusto Righi. Depressing the key closed the circuit and
brought the inductor coil into action. Vivid sparks occurred between
the balls of the oscillator, to the accompaniment of a succession of
sharp cracks, like the reports of a pistol, and some energy was sent
off the square metal plate in the form of trains of electromagnetic
waves, which radiated out in all directions. But the energy occupied
a very large bandwidth and the receivers of that period could not
separate two transmissions. William J. White of the Post Office wrote
in 1908, "The chief objection which has been raised against modern
wireless telegraphy is its want of secrecy. With a transmitter
sending out waves in all directions, it is possible for unscrupulous
persons to receive the messages and make an improper use of them.
This form of 'scientific hooliganism' has, in fact, become somewhat
notorious. When two or three transmitters are each sending out their
electromagnetic waves, the result, naturally, is utter confusion."
White added that the British Postal Administration was refusing to
grant licences for more than one system in the same area, in spite of
the fact that there had been some 'alleged' solutions of the problem.
The phenomenon of resonance was known and Dr (later Sir Oliver) Lodge
had taken out various patents between 1889 and 1898 in connection with
receivers. Marconi and his assistants ultimately solved the problem
by modifying Lodge's syntonic Leyden jar tuned circuit. They added a
tapped inductance in the aerial circuit of the transmitter and used
variable capacitors instead of fixed ones. This was probably the most
significant modification made in the development of wireless
telegraphy. (In Greek the word syntonismos 'to bring to equal tone'
is used for 'tuning'.)
Public-domain text, read in full here on John Shaqi.
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