Radar Personalities
Guglielmo Marconi
The following article appeared in Electronics Weekly, June 5 1996:
100 years ago this man set wireless alight
In
June 1896, Guglielmo Marconi filed a patent which is widely recognised as the
birth of radio communications. Tom Ivall tells the story.
When Guglielmo Marconi applied for a patent on his wireless telegraphy apparatus exactly a hundred years ago he was in effect announcing the start of an era.
Electromagnetic radiation outside the visible spectrum could now be utilised as an aid to human communication. It was the beginning of a new technology and also a commercial enterprise.
British Patent No. 12039, "Improvements in transmitting electrical impulses and signals and in apparatus there-for", application date 2 June 1896, was the world's first radio patent. Queen Victoria was still on the throne.
Physicists and others had already been experimenting with this form of radiate energy for a decade or more, though without fully understanding what they were dealing with. They certainly had no practical applications in mind. Branly in France, Hughes and Lodge in England, Popov in Russia and Thomson in America, among others, had all detected apparent radiation from electrical discharges, but it was not explored much further.
The electron was as yet unknown. Certainly Maxwell had defined the conditions for the propagation of electro-magnetic waves as early as the years 1861-1865. His Royal Society paper "A dynamical theory of the electromagnetic field" was to become a scientific classic.
But the experimental physicists of the time were either unaware of it or sceptical of what they considered a dubious concept. Helmholtz in Germany, however, eventually understood the importance of this mathematically based theory. It was under him, in Berlin, that Heinrich Hertz was then working as an assistant professor. Helmholtz realised that the theory needed experimental verification and invited Hertz to attempt it.
Hertz generated electro-magnetic radiation with an induction coil, a spark gap and what we now call a dipole aerial. He detected it with a tuneable loop resonator containing another, very small, spark gap. He demonstrated that the radiation had the characteristics of waves and, like light, could be reflected, refracted, diffracted, polarised and made to produce interference patterns. His method was to set up standing waves with a sheet metal reflector and locate their nodes with the loop resonator. Thus he validated Maxwell's theory.
Hertz's laboratory experiments were recognised everywhere. Branly, Lodge and Popov among others immediately repeated them and gave demonstrations to scientific and. non-technical audiences. Yet despite the fact that telegraphy existed and some of its pioneers like Morse and Preece had long been seeking a wireless version, few seemed to realise that the Hertzian waves, as they became known, were offering them a potent new means of electrical signaling.
One of the scientists who followed up Hertz's experiments, however, was Righi at Bologna University. Marconi, then a teenager living near Bologna, had attended his lectures and studied his writings on EM radiation. This was the start of Marconi's interest in Hertzian waves.
But it was later, in 1894, after reading more about Hertz's work, that he became fired with the idea of using these waves for communication. Then began the famous series of radio signaling experiments at his home in 1895.
These experiments at Bologna used apparatus broadly similar to at of the physicists who had followed Hertz's work. The transmitter was a keyed induction coil producing high-voltage pulses, a spark gap and a short Hertzian, or half-wave, dipole aerial. The receiver was little more than a dipole aerial with a non-rectifying detector.
Initially, the ranges achieved were very short up to about 100m. But then Marconi had the idea, suggested by Popov's experiments in detecting distant thunderstorms, of replacing the Hertzian dipole in both transmitter and receiver with an elevated electrode, or antenna, on one side and an earthed metal plate on the other.
These modifications gave a tremendous increase in range - eventually, with an 8m high antenna, to about 2.4km. Thus Marconi had devised what is now called the quarter-wave monopole, or Marconi aerial, in which a reflection or image of the quarter-wave element corresponds to the lower element of a vertical half-wave dipole. Some consider this to be his most important contribution to radio technology.
An interesting footnote is that acceptance of Marconi's first patent in July 1897 provided the commercial basis for setting up a company that same month to develop and pro-mote the Marconi apparatus. This was The Wireless Telegraph and Signal Company Limited, which eventually became The Marconi Company and finally part of GEC.
(This is an extract from an article published in the June Issue of Electronics World)
The article above appeared in Electronics Weekly, June 5 1996.
You can down load an Acrobat format (.pdf) article titled "Guglielmo Marconi and Early Systems of Wireless Communication" by R.W. Simons here.
