Radio

  
Electromagnetic Waves 
Journalism 

 
Library of American Broadcasting 
Web Page of University of Maryland's extensive collection. 
Federal Communication Commission 
Website for US government agency that protects public interests in communications. 
CRTC 
Website of the Canadian Radio-Television and Telecommunications Commission. 
Sounds of Broadcasting History 
Hear history happening. From Texas Wesleyan University. 
100 Years of Radio 
Extensive library of information on Marconi and Amateur Radio.

propagate 

CB Radio 
CB (Citizens’ Band) Radios are used by truckers and taxi drivers, emergency personnel and by private users for weather reports and emergencies. Broadcast authorities, such as Canada’s CRTC or United States’ FCC allocate certain radio frequencies  for citizen’s band, radio dispatch systems, and paging services. 

CB is an amplitude modulated (AM) broadcast system for non-commercial purposes. Many units are designed for automobiles. They consist of a microphone, a transceiver (device to transmit and receive the radio waves) and an antenna. The transceiver broadcasts in all directions, so anyone can listen within the available range (usually 10 to 100 miles). The transmissions are simultaneous; you can’t talk and listen at the same time. Receiving the broadcast works just like on an FM/AM radio. 

If you simply want to listen, you can purchase a scanner to monitor channels. This is particularly useful for journalists to immediately know when an accident has taken place by listening to police and fire channels. 

Beepers 
The same concepts are used for beepers, small receivers that send one-way signals to notify the user of something, usually when someone is trying to reach you. Beepers often run on the same frequency, but only react to a unique identification number. Some beepers can display short "alpha-numeric" messages. In most cases, you can "beep" someone by calling a phone number and requesting an alert signal be broadcast to that person’s beeper. When the person receives the notification, he or she can go to a telephone and contact the caller. 

AM/FM radio 
One of the most common and obvious uses of radio are AM/FM broadcast radios, found in cars and stereos. There are hundreds of radio stations in North America, offering music, "phone-in" talk shows, and information like news and weather reports. Almost every place on earth is bombarded with electrical signals from radio and television stations, which remain unheard unless they are processed with three key components: an antenna, a tuner, and an amplifier. 

An antenna is the first step in receiving the transmission. As the signals in the air strike the antenna, energy is transferred into it. These impulses travel down to a tuner, which eliminates "noise ". This noise comes from unwanted signals on another frequency (or "station"). The user selects a certain station, and all signals not originating from that frequency are shut out. But the signals still aren’t strong enough to hear, they must first be amplified. The amplifier increases the strength of the signal to bring the sound within hearing range. 

Most radios allow you to listen to AM and FM stations, but you need to flip a switch to tune into FM stations, and flip it back for AM stations. When you turn the tuner knob on your radio, you are choosing a particular carrier signal. The carrier wave is then modulated by the sound signal. An AM station modulates the amplification of the signal; the size of the voice or music. FM stations modulate to the same frequency as the original sound, resulting in better sound reproduction. 

Shortwave Radio 
While various radio bands (short-wave, long-wave, medium-wave, very-high frequency, and ultrahigh frequency) are allocated for specific applications, short-wave is for radio broadcasts in the high-frequency range of 3 to 30 MHz, and can be received a long distance away. It is commonly used for amateur or "ham" radio, though some medium-wave band frequencies have also been allotted for this purpose. They have been extremely helpful when other forms of communication have been disrupted because of disasters such as wars. For ham radio operators, the hobby is a gateway to the world, where they can communicate with people from all over. 

History 
While most of the information related to electromagnetic waves was discovered inadvertently by scientists studying electricity, radio history begins in 1873 when British physicist James Clerk Maxwell published his theory on electromagnetic waves. His theory was mainly targeted at light waves, but 15 years later Heinrich Hertz applied the findings by generating the waves electrically. He supplied an electric charge to a capacity, which he then short-circuited through a spark gap. An electric discharge resulted, building up an opposite charge on the capacitor, and surging back and forth creating an oscillating  electric discharge in the form of a spark. Energy from this oscillation radiated from the spark gap as electromagnetic waves, which Hertz measured to determine wavelength and velocity . The findings were not entirely new; the concepts were already applied using light to carry Morse code, but the research was still quite valuable. Electromagnetic waves are superior to light waves because they can travel long distances and still be understood. 

Italian electrical engineer Guglielmo Marconi is considered the actual inventor of the radio. Starting in 1895 he began to completely enhance practically every aspect of the technology. Using an ordinary telegraph key as a transmitter, his implementation of the radio transmitted signals exceeding 1.6 km (about 1 mile). In 1897 he managed 29 km (18 miles) from a ship at sea, and in 1899 established a commercial communication system between England and France. In 1901 he was able to receive signals 322 km (200 miles) away, but his true feat was sending a single letter across the Atlantic Ocean from what is know known as Signal Hill in Saint John’s, Newfoundland, Canada that same year. In 1902 messages were regularly send across the Atlantic, and by 1905 it commonly became a much-needed form of communication for ships and shore stations. For his work in the field, he received a Nobel Prize in physics in 1909 alongside German physicist Karl Ferdinand.