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 (seen above), 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.
Gugliemo
Marconi's invention. The system was called "wireless telegraphy", and the terms
"radio" and "wireless" are still used interchangeably today.
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.
Radio & Ham Radio
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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 (on page 2) overviews frequency band designations and its utilization.
