Radio communication
is among the easiest forms of communication to produce and can be the most useful method of communication in times of area-wide trouble. The phenomenon has been with us for almost a century and it is still widely used for entertainment and other useful things today.
In the Beginning
Radio communications is a nebulous term that encompasses a great many methods of achieving the same thing. Radio communication has its beginnings with two different men. Many of us have heard of Guglielmo Marconi, the Italian inventor who developed the ability to send messages without the need for wire or other media. Marconi is most famous for this one invention and is usually the only person given credit for the development of radio communication. At around the same time, however, there was an American working on the same process. Nathan Stubblefield, a melon farmer from Murray, KY, also developed wireless communication.
No matter who came first, however, wireless or radio communication stuck in the American and European cultures and has been with us ever since. The methods and equipment have changed rather drastically over the century or so of its known existence. The principle, when you see it on paper in a block diagram form, is rather simple to follow. Let's first look at the two main forms of getting a signal to an ordinary radio: AM and FM.
Would You Like That Signal Scrambled or Fried?
AM, or amplitude modulation, uses the radio wave's size as the power source that pushes the signal off of the tower toward the receivers. The speed of the waves is measured in kilohertz. Increasing the speed (or frequency) is accomplished by causing the signal coming into the transmitter (usually audio of some sort) into the system and combining the audio with the waves generated by the transmitter (in a component known as an exciter). The result is a mixed signal of audio and transmission power pushed up the transmitting antenna and out into the world. AM radio was the original form of radio both Stubblefield and Marconi produced, and its first commercial use in America began with station KDKA out of Pittsburgh, PA---a station still in operation.
FM, or Frequency Modulation, uses the speed of the wave to take the signal as far as possible---often despite its amplitude. FM transmitters create with their power source what's called a "carrier wave," which is a signal at the frequency of the receiving station (for example 98.7 MHz). Again an exciter is used to put the audio input together with the carrier wave to produce an FM signal with the audio on board. FM came to being as early as the late 1950s. It languished as second to the AM band until the 1970s, when the population discovered clear, stereo audio coming out of their radios. FM is the most popular form of transmission and is used in several ways in our everyday lives.
Hand Me the Transmitter, Please
Many objects used in daily life involve FM transmission. For instance, the cordless telephone uses frequency modulation to get the signal to and from the base to the handset. The frequencies these days range in the gigahertz (GHz) or thousands of megahertz. Such high frequencies are used to keep your conversations private and unable to be picked up by everyday radios. Another use of FM is the small transmitter used to send the signal from your MP3 player to your car radio so that you can listen to your own music or audio books while driving. The transmission range of these units is very limited, but effective in the right circumstances. Many MP3 players today also have circuitry for an FM receiver built in, so that you can listen to the FM band rather than just what's on your player.
Another form of radio communication is amateur, or HAM, radio. The form of personal audio transmission and reception is, as are commercial AM and FM bands, licensed for use by the Federal Communications Commission (FCC). HAM radio is used as a personal communication with friends and acquaintances across the country---or around the world---using Morse code and voice communication. (Morse cold isn't used as widely anymore, as voice transmission has improved over the last 20 years.) The equipment needed includes a radio, a power supply (within the confines of the class of your license) and an antenna. There are several bands in HAM radio that are designated by the size of the radio wave produced to cause communication to happen. For instance, the 2-meter band, by far one of the most popular bands, uses FM to send a 2-meter wave at about 144,500,000,000 times per second. Amateur radio is also extremely handy in emergency situations when power is out and communications need to be made to and from emergency services.
Another use of radio communication most aren't aware of is television. While TVs and radios appear to be different things, the TV transmitter simply broadcasts different material. The rule of thumb is that TV transmitters use AM to transmit the moving pictures and FM to transmit the sound, though this is an over-simplified description of how a TV transmitter works.
Finally, the last component necessary to achieve radio transmission is the antenna. There is a saying in amateur radio: "Height is everything." In essence that's right for FM transmission at any level. FM transmission is knows as a "line of sight" broadcast method, meaning the signal should pass relatively unchallenged by natural or man-made objects in its path. AM's broadcast method simply sprays signal is all directions, usually with more concentration in a given direction. The AM signal surrounds everything in its path. This is why, if you live near a transmission tower, you're more likely to hear the AM signal coming from your toaster or curling iron than you would the FM signal. The important factor in an antenna being useful is what's known as the "gain" of an antenna. Gain, which means the voltage present when the signal is applied to it, is usually the deciding factor in how strong your AM signal is or how far your FM signal can reach. Antennas are a science unto themselves, and we only need to know that the height and gain of a transmission antenna are the important keys to radio communication.
Radio is, by and large, is the most trusted and useful form of broadcasting in existence today. AM, in particular, has many advantages over FM (in that you can take a penny and a nickel to create an AM receiving antenna). Whether for personal pleasure or for emergency communications, radio is among the most affordable and achievable methods of communication.
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