History of Radio

Hans Christian Orsted (1777--1851) Danish Physicist/chemist

• Discovers electric currents create magnetic fields (important aspect of electromagnetism)

• Inspired by Kantian philosophy on the unity of nature (I.e. that a connection between electricity and magnetism

• April 21, 1820 at U of Copenhagen as a professor of physics he notices a compass needle deflected from magnetic north when an electric current from a battery was switched on and off

• Findings influence French physicist Andre-Marie Ampere…and his findings represent major step toward unified concept of energy

Andre-Marie Ampere - 1775-1836 French physicist

• Often referred to as discoverer of electromagnetism

• SI unit of measurement of electric current (ampere) named after him

• One week after Orsted discovery publishes paper at polytechnic school at Paris an complex explanation of Orsted’s discovery and even predicted further discoveries

• He demonstrated on that same day that parallel wires carrying currents attract or repel each other, depending on whether currents are in the same (attraction) or opposite directions (repulsion)

• Electrodynamics (what he referred to his studies)

Electromagnetic induction

• is energy of voltage across a conductor moving through a magnetic field. It underlies the operation of generators, all electric motors, transformers, induction motors, synchronous motors, solenoids, and most other electrical machines.

• Michael Faraday (1791-1867-- British chemist/naturalist) is generally credited with the discovery of the induction phenomenon in 1831 (though it may have been anticipated by the work of Francesco Zantedeschi in 1829)

EMF (Electromotive Force)

• Faraday (with little formal education or higher mathematics training) found that the electromotive force (EMF) produced around a closed path is proportional to the rate of change of the magnetic flux through any surface bounded by that path.

• In practice, this means that an electric current will be induced in any closed circuit when the magnetic flux through a surface bounded by the conductor changes.

• This applies whether the field itself changes in strength or the conductor is moved through it.

• Einstein kept of photo of him in his office, and he (Faraday) is considered one of the best “experimentalists” in science

James Clerk Maxwell (1831-1879) Classical Electromagnetic theory

• James Clerk Maxwell (13 June 1831 – 5 November 1879) was a Scottish theoretical physicist and mathematician.

• His most important achievement was formulating classical electromagnetic theory. This united all previously unrelated observations, experiments and equations of electricity, magnetism and even optics into a consistent theory.

• His findings predict the existence of electromagnetic WAVES

• His set of equations—Maxwell's equations—demonstrated that electricity, magnetism and even light are all manifestations of the same phenomenon, the electromagnetic field.

• Subsequently, all other classic laws or equations of these disciplines were simplified cases of Maxwell's equations. Maxwell's work in electromagnetism has been called the "second great unification in physics", after the first one carried out by Isaac Newton.

Radio-Frequency Induction or RF induction

• Radio-frequency induction or RF induction is the use of a radio frequency magnetic field to transfer energy by means of electromagnetic induction in the near field.

• A radio-frequency alternating current is passed through a coil of wire that acts as the transmitter, and a second coil or conducting object, magnetically coupled to the first coil, acts as the receiver.

The evolution of radio…

• In the late 19th century it was clear to various scientists and experimenters that wireless communication was possible. Various theoretical and experimental innovations led to the development of radio and the communication system we know today

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13 years of activity in radio research….

• 1872 William Henry Ward receives US Patent for radio development

• 1875 Edison while experimenting with telegraph notes phenomenon he terms “etheric force” (ridiculed)

• 1878 David E. Hughes notices that sparks can be heard in telephone receiver when experimenting with his carbon microphone. Eventually can detects signals over 200 yards

• 1884 Calzecchi-Onest in Fermo Italy invents a primitive device that responds to radio waves -- tube filled with iron filings, called a “coherer.” Critical discovery that will become the first practical radio detector.

• 1885 Edison takes out US Patent on radio communication system between ships (later sells to Marconi -- not based on electromagnetic wave reception)

So who invented radio?

• Disputed claims … called “wireless telegraphy.”

• Actually many scientist are involved…

• Key invention (spark-gap transmitter) to wirelessly transmit data using the entire frequency spectrum

• 1893 Nikola Tesla demonstrates public wireless radio communication (took out several patents)

Coherer / Edouard Branly

• The coherer was a primitive form of radio signal detector used in the first radio receivers during the wireless telegraphy era at the beginning of the twentieth century. Invented around 1890 by French scientist Édouard Branly,

• It consisted of a tube or capsule containing two electrodes spaced a small distance apart, with metal filings in the space between them. It was a key enabling technology for radio, and was the first device used to detect radio signals in practical spark gap transmitter wireless telegraphy.

Jagdish Chandra Bose

• 1894 - Indian physicist demonstrates radio waves in Calcutta (so that others can add to research) by igniting gunpowder and ringing a bell

• Worked under very difficult conditions at St. Xavier’s in Calcutta

• Refused his salary for three years (Rs 200 -- Rs 300 for Europeans)

• Spent his own money on experiments, not motivated to patent

• Adrisya Alok (Beng. “Invisible Light”) can easily pass through brick walls, etc.

• 1896 - Meets Marconi in London• Expresses disinterest in commercial

use of telegraphy• First to use a semiconductor

junction to detect radio waves, invented various now commonplace microwave components

• 1977 - Sir Nevill Mott, Nobel Laureate “JC Bose was 60 years ahead of his time…he had anticipated the existence of OP-type and N-type semiconductors.

Guglielmo Marconi (1874-1937) radio telegraph system

• 1896 awarded British Patent for radio (using earlier techniques -- Tesla, etc.)

• 1897 Established radio station at Niton, Isle of Wight, two US Patents

• Radio factory opened in Chelmsford, England, employs 50 people

British Marconi

• 1904 US Patent Office reverses decision, awards Marconi patent for invention of radio

• Possibly influenced by Marconi’s backers (Edison and Andrew Carnegie)

• Allowed US Govt. to side-step of Tesla’s royalty claims

• 1897 British Marconi established and subsidiary American Marconi has stranglehold on ship to shore communication.

• Like ATT, owns all equipment, refuses communication with non-Marconi equipped ships