Radio waves travel at 186,000 miles per second through air. In contrast, sound waves travel at only 1/5 of a mile per second. If a modulation is made of the radio wave that exactly reproduces the amplitude and frequency characteristics of the original sound wave, then sound can be transmitted rapidly over long distances. This leads to a very interesting phenomena. During a live broadcast in New York, the music will reach listeners in California a fraction of a second before it can be heard by the New York audience sitting in the back of the concert hall.
Radio transmissions are a combination of two kinds of waves: audio frequency waves that represent the sounds being transmitted and radio frequency waves that “carry” the audio information. All waves have a wavelength, amplitude and a frequency as shown in the figure. These properties of the wave allow it to be modified to carry sound information. In AM (amplitude modulation) radio transmissions, the amplitude of the combined audio frequency and radio frequency waves varies to match the audio signal.
AM radio is subject to problems with static interference. Electromagnetic waves (like radio waves) are produced by the spark discharges in car ignition systems, brushes of electric motors and in all sorts of electrical appliances, as well as in thunderstorms. There is considerable background noise that changes the amplitude of the radio wave signal adding random crackling noises called static. In FM (frequency modulation) radio transmissions, the frequency of the combined waves changes to reproduce the audio signal.
For example, higher frequency is associated with the peak amplitude in the audio wave. FM waves do not have a problem with interference because the noise background does not modify the radio wave frequency. In addition FM waves give better sound reproduction. Inventor Ernst Alexanderson was the General Electric Engineer whose high-frequency alternator gave America its start in the field of radio communication. During his 46-year career with G. E. , Swedish-born Alexanderson became the company’s most prolific inventor, receiving a total of 322 patents.
He produced inventions in such fields as railway electrification, motors and power transmissions, telephone relay s, and electric ship propulsion, in addition to his pioneer work in radio and television. In 1904, Alexanderson was assigned to build a high-frequency machine that would operate at high speeds and produce a continuous-wave commission. Before the invention of his alternator, radio was an affair only of dots and dashes transmitted by inefficient crashing spark machines.
After two years of experimentation, Alexanderson finally constructed a two-kilowatt, 100,000-cycle machine. It was installed in the Fessenden station at Brant Rock, Massachusetts, on Christmas Eve, 1906. It enabled that station to transmit a radio broadcast which included a voice and a violin solo. Alexanderson’s name also will be recorded in history for his pioneer efforts in television and the transmission of pictures. On June 5, 924, he transmitted the first facsimile message across the Atlantic.
In 1927 he staged the first home reception of television at his own home in Schenectady, New York, using high-frequency neon lamps and a perforated scanning disc. He gave the first public demonstration of television on January 13, 1928. The invention of the Radio and discovery of Radio waves was very important to modern culture; they were used as a basis of communication for Morse code and helped to communicate during the war. Nowadays, Radio waves are still widely used by many companies for communication.
