INTRODUCTION TO RADIO

Invention of radio

Many people were involved in the invention of radio in its current form. Experimental work on the connection between electricity and magnetism began around 1820 with the work of Hans Christian Ørsted, and continued with the work of André-Marie Ampère, Joseph Henry, and Michael Faraday. These investigations culminated in a theory ofelectromagnetism developed by James Clerk Maxwell, which predicted the existence of electromagnetic waves.

Maxwell published A Treatise on Electricity and Magnetism in 1873, stimulating many people to experiment with wireless communication. Others experimented without the benefit of his theories. It is considered likely that the first intentional transmission of a signal by means of electromagnetic waves was performed by David Edward Hughes around 1880, although this was considered to be induction at the time. The first systematic and unequivocal transmission of EM waves was performed by Heinrich Rudolf Hertz and described in papers published in 1887 and 1890. Hertz famously considered these results as being of little practical value.

After Hertz's work many people were involved in further development of the electronic components and methods to improve the transmission and detection of electromagnetic waves. Around the turn of the 20th century Guglielmo Marconi, developed the first apparatus for long distance radio communication.

 On 23 December 1900, Reginald A. Fessenden became the first person to send audio (wireless telephony) by means of electromagnetic waves, successfully transmitting over a distance of about 1.6 kilometers, and six years later on Christmas Eve 1906 he became the first person to make a public radio broadcas

Wireless signalling methods

Several different electrical, magnetic or electromagnetic physical phenomena can be used to transmit signals over a distance without intervening wires. The various methods for wireless signal transmissions include

• Electrical conduction through the ground, or through water.
• Magnetic induction
• Capacitive coupling
• Electromagnetic radiation

All these physical phenomena, as well as various other ideas such as conduction through air, were tested for the purpose of communication. Early researchers may not have understood or disclosed which physical effects were responsible for transmitting signals. Early experiments used the existing theories of the movement of charged particles through an electrical conductor. There was no theory of electromagnetic wave propagation to guide experiments before Maxwell's treatise and its verification by Hertz and others.

Capacitive and inductive coupling systems today are used only for short-range special purpose systems. The physical phenomenon used today for long-distance wireless communications involves the use of modulated electromagnetic waves, which is radio