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Radio is the branch of telecommunication that involves the propagation of electromagnetic waves through space.

Many scientists dreamed of discovering a way to wireless communication, but never succeeded until the late nineteenth century. James Clerk Maxwell developed the first radio-wave theorem in 1864. He proved, mathematically, that if an electrical interruption is of short distance from the point at which it occurred, there would be effect or passage of electrical current due to "some sort of waves that move at the speed of light", in which the electromagnetic energy would travel. Heinrich Hertz experimented with Maxwell’s thesis in 1888. He demonstrated that "waves traveled in straight lines and that they could be reflected by a metal sheet". He tested with two conductors separated by a short gap (5ft). This idealism was advanced by the Italian physicist Guglielmo Marconi, who repeated Hertz’s experiments with a spark gap of 30ft and succeeded.

Augusto Righi, an Italian physicist, continued and refined Hertz’s work establishing the equality between electrical and optical vibrations. Another scientist, Temistocle Calzecchi-Onesti, constructed, in 1888, a "tube" due to his belief that electrical discharges of atmospheric perturbations influence iron filings.

In 1894, Oliver Lodge named Temistocle’s famous "tube" the "coherer" and increased the reception gain of the hertzian waves. All that was left was the Russian, Popov (Alexander Popoff), to create a vertical metal pole by using Lodge’s coherer and collecting atmospheric disturbances in a rudimentary antenna. The invention of these instruments helped Guglielmo Marconi’s discovery. Marconi verified that electromagnetic waves travel between two points separated by an obstacle. This led to the creation of the first radio transmitter…This experiment was repeated with larger spark gaps (started with 5 ft; expanded to 100 km). Radiotelegraphy was born.

The Invention of AM & FM

The first radio station began operation in the 1920’s. The broadcasting radio station was KDKA in Pittsburgh. This service became very popular and soon spreaded around the globe.

Europe and North Americas’ dissatisfaction with the medium-wave band of frequencies for providing broadcasting channels motivated the usage of shortwaves, which provided greater audio frequency and a diversity of broadcasting channels. This is what distinguishes transmission bands nowadays.

There are two distinct radio transmission bands:

AM
(amplified modulation) - varies the strength (amplitude) of a signal. Refers to the height of the wave.

FM
(frequency modulation) - varies the frequency of a signal.

These radio bands were named for the method used to superimpose an audio signal on a radio wave.

As mentioned earlier, the medium-wave band (AM) was the mostly used band of frequency in the 1900s. The radio, in that time, was only used to transmit important messages or speeches that involved the war (World War I). It wasn’t until the 1920s when broadcast radio stations took an interest in broadcasting entertainment. More and more radio stations were established and began focusing on entertainment. The United States and Europe wanted to expand the broadcast channels. This encouraged the usage of shortwaves (FM). By 1948, there appeared to be approximately 1,000 FM stations operating or licensed. Nowadays, approximately 6,700 FM stations are operating. Throughout the years, especially during the 70s, the FM band became more and more popular, particularly among young listeners, while AM only attracted elders due to the fact that it’s an outlet for news and information.

The difference between FM and AM is notable. First of all, the frequency modulation band has a frequency range of 88 to 108 MHz* (short wave); however, the amplitude modulation’s frequency ranges from 540 to 1700 kHz* (medium wave). Only 10 kHz is assigned to radio stations that use AM; for those that use FM, 200 kHz per station. Table 1-1 overviews frequency band designations and its utilization.

* kHz (kilohertz) means that there will be thousands of cycles per second.
* MHz (megahertz) means that there will be millions of cycles per second.
* GHz (gigahertz) means that there will be billions of cycles per second.