Many people hear the name Marconi and attribute the invention of radio to him. It is probably more accurate to say that Guglielmo Marconi discovered a way to manipulate and exploit radio frequency energy. Marconi was actually one of many experimenters who were trying to send signals through the air thus the name wireless. The actual roots of radio can be traced back to the early 1800's when Michael Faraday who was in England and Joseph Henry who was in America developed the theory of inductance. This theory said that an electrical current flowing through one wire could create or induce a current to flow in a separate wire. Henry was always slow in publishing his results and he was unaware of Faraday's work. Ultimately Faraday was recognized as the discoverer of mutual inductance (the basis of transformers), while Henry is credited with the discovery of self-inductance. The unit of inductance, called "the henry" immortalizes his name to this day.
In 1887 a German physicist named Heinrich Hertz came up with the first reasonable explanation for what was going on with his demonstration of the existence of electromagnetic waves of energy. The standard unit of frequency is named Hertz after the man who discovered the waves of energy. A frequency of 1 complete cycle per second is a frequency of 1 Hz. In radiocommunication, signals are typically thousands, millions or billions of hertz in frequency. A frequency of 1000 Hz is called 1 kilohertz (1kHz). A frequency of 1000 kHz is 1 megahertz (1MHz). A frequency of 1000 MHz is 1 gigahertz (1GHz) and so on through the metric scale of measurement.
In 1892, a French physicist named Edouard Branley invented the first receiver of electromagnetic waves called a "Coherer" Branley found that a nearby electromagnetic disturbance such as a spark or a radio wave known as a Hertzian wave caused by a spark would lower the resistance of a thin layer of platinum deposited on a glass, thus the coherer wireless detector. Branley took the experiment one step further and discovered that the variations in the resistance of metals in a finely divided state such as metal filings were even more responsive to electromagnetic energy.
Marconi followed these developments and in 1895 created his first successful wireless system. He patented his invention in England in 1896 and pursued the commercial aspects of wireless by installing his system on ships and at shore stations. On December 12, 1901, Marconi sent a signal from St. Johns Newfoundland to Poldhu, England. It consisted only of the letter S sent in telegraphic code but it was the first transatlantic broadcast of an electromagnetic signal or radio wave. Interest in radio began to grow!
Marconi's radio station in Poldhu, England.
In 1905, Sir Ambose Fleming developed the Diode Electron Tube which permitted the detection of high frequency radio waves. This was a vast improvement over the Branley Coherer. Fleming called this device a valve that controlled the flow of electrons in a circut. Often today tubes are referred to as valves in England after the original Fleming valve!
While Marconi was transmitting the dots and dashes of telegraphic code, another scientist, Canadian Reginald A. Fesseden, was pursuing a much loftier goal. Fesseden wanted to transmit the human voice and music without wires. Fesseden was the head of the electrical engineering department at the University of Pittsburgh when he developed a more effective way of sending information over the airwaves. Fesseden devised the theory of the "continuous wave," a means of superimposing sound onto a radio wave. This sound could then be transmitted to a receiver. After years of experimentation, on December 23, 1900, he successfully ransmitted the sound of a human voice between two 50 foot towers. Fesseden beamed the first long range transmissions of voice on Christmas Eve, 1906, from a station in Massachusetts. This first radio program featured the inventor playing "O Holy Night" on his violin, then singing carols with his wife and a friend. Hundreds of miles out in the Atlantic, astonished ship radio operators heard the Christmas music. Fesseden never achieved the fame of Marconi and others but he truly is the father of Broadcast Radio.
Fesseden's radio tower at Cape Dodd Massachusetts.
In 1906, Lee De Forest invented the Audion, the first Triode Electron Tube to successfully amplify radio waves. De Forest has been labeled one of the fathers of the electronic age since the audion helped start the explosion of electronics earlier this century. De Forest invented the device in 1906 by inserting a grid into the center of a vacuum tube. Applying voltage to the grid controlled the amount of a second current flowing through the tube. In 1913, AT&T installed audions to boost voice signals as they crossed the United States. This invention made coast to coast telephone calls possible. Soon, this triode tube was being used in radios as well.
DeForest's first Audion.
In 1918, Edwin Armstrong developed the superhetrodyne receiver circuit. A superhetrodyne circuit uses one or more local oscillators and mixers to obtain a constant frequency signal. A fixed frequency signal is much more easily processed then a signal that changes frequency. Radio receiver tuning and adjustment was now a simple process and this made radio accessible to the average individual, and thus commercial broadcasting was born. In 1933, Armstrong developed yet another significant improvement to radio. Frequency Modulation or FM. This mode of radio transmission allowed for reduced noise and interference. Development of FM and the experimentation in the higher frequencies lead to the VHF and UHF regions of the radio spectrum being used today.
World War II brought further advances in radio technology. The war years gave birth to the Voice of America or VOA. Shortwave radio was a powerful tool for information and propaganda during the war. When the war ended, a new aspect of the radio hobby started. Many excellent transmitters and receivers became available to the hobbyist by way of the surplus market. Military radio technology also filtered down into the commercial radio market. After the war, many radio applications beyond broadcasting began to emerge. Public safety and business radio applications started to grow.
The invention of the transistor by American physicists John Bardeen, Walter Brattain, and William Shockley was announced by Bell Telephone Laboratories in 1948. These men were later jointly awarded the Nobel Prize for their invention. Shockley's further improvements in 1952 ushered in a whole new era of electronics and further improvements in radio transmitter and receiver designs. Vacuum tubes have an inherent problem do to their design. The heat generated by the tubes causes frequency drift in even the most sophisticated receivers. Circuits designed with transistors greatly improved this problem. The late 1950's found the country amazed by pocket size radios. But there was much more to come!
In 1959, Robert Noyce at Fairchild Semiconductor and Jack Kirby at Texas Instruments, independently developed the first integrated circuits when they created networks of transistors on a single "chip." by the late 1960's, entire radio receiver circuits could be placed on individual chips. further developments in integrated circuitry that improved frequency synthesis and signal filtering came about as the result of the integrated circuit. The microprocessors that became available in the 1970's brought us into the world of digitally controlled electronics including computers. A modest cost receiver of today contains high performance features that would have cost thousands of dollars years ago.
We have the ability to use inexpensive receivers to allow us to listen in on thousands of signals bringing every facet of the world into our homes. Still, when you hear a rare station on the air it's fun to think of Marconi, Fesseden, Armstrong and all the others who gave us the gift of radio.
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