The Invention of the Radio - pages 1 & 2
(Located at http://library.advanced.org/27887/gather/history/radio.shtml)
Radio is the branch of telecommunication that involves the propagation of electromagnetic waves through space.
How did the Radio Originate?
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 Maxwells 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 Hertzs experiments with a spark gap of 30ft and succeeded.
Augusto Righi, an Italian physicist, continued and refined Hertzs 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 Temistocles 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 Lodges coherer and collecting atmospheric disturbances in a rudimentary antenna. The invention of these instruments helped Guglielmo Marconis 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 1920s. 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 wasnt 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 its 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 modulations 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.
time signals, standard frequencies
Very Low Frequency (VLF)
3 30 kHz
|navigational, radio broadcasting||Low Frequency (LF)||30 300 kHz||10,000 1,000m|
|land, radio broadcasting, maritime mobile||Medium Frequency (MF)||300 3,000 kHz||1,000 100m|
|mobile, radio broadcasting, amateur||High Frequency (HF)||3 30 MHz||100 10m|
|radio navigation, mobile, amateur, radio and TV broadcasting||Very High Frequency (VHF)||30 300 MHz||10 1m|
|space communication, aeronautical mobile, amateur, meteorological||Ultrahigh Frequency (UHF)||300 3,000 MHz||1m 10cm|
|radio location, space communication, navigation, mobile||Superhigh Frequency (SHF)||3 30 GHz*||10cm 100cm|
* 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.
Ham or Amateur radio is a community of radio operators that use transmitters and receivers to communicate with other amateur operators. Youre probably wondering why is it called "ham"? According to G. M. Dodge's The Telegraph Instructor "Ham means a poor operator. A 'plug." For others, the origin of ham was never found. Therefore a compromising explanation for the integration of this word in this term was concluded nobody knows why.
There are around 600,000 amateur operators in the United States. These amateur operators or hams can do just about anything they please through the radio, although, they have a couple minor restrictions or constraints, such as, broadcasting messages to the public and using the radio for making money in any way. Other than this, they can do many beneficent things on the radio.
Amateur operators of HF radios can communicate with other hams worldwide; those who own VHF or UHF transceivers can talk to people in their local community. The radios can also be used for emergencies -of any kind- when other communication systems fail or go out. Hams can also establish satellite communications. They even have their own easy to use satellites!
There are other numerous things you can do through the radio. All you have to be is a ham. (You become one by getting licensed by the FCC.)