The invention of radio is credited to Italian mastermind Guglielmo Marconi, who first sent wireless messages in 1896. Though these first transmissions extended only a mile, different methods of signal transmission were quickly developed. Radio messages can be sent in a variety of ways, each with certain advantages and disadvantages.
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The single sideband method of radio communication uses one half of a radio wave to deliver a message. When a radio emits electromagnetic waves at a certain frequency, waves slightly above and below the target band are also influenced. These "sidebands" contain a copy, or "echo," of the main message.
With the single sideband method, circuits are used to eliminate one of these copied signals. The remaining sideband loses signal quality but receives a boost in transmitting power. Because of this increase in signal power, the single sideband method of radio communication is able to send messages over long distances. This method is commonly used by military units and isolated vessels at sea.
Radiotelephony is the proper name for the transmission method most commonly called "radio" today. With radiotelephony, audio waves from an input source or a microphone are converted into electrical waves. Amplifiers take this signal and increase the power. The audio message is contained in this modulating signal, which can be received through the air.
When a radiotelephony signal is picked up by a receiver, the process is reversed. The modulated signal is decoded and brought down to a standard power strength. Finally, the signal is converted back into audible sound through a speaker. This method of radio communication permits a high-quality audio signal to be sent over relatively short distances.
The radiotelegraphy method of radio communication relies on starting and stopping the main radio signal, called the "carrier." During most radio transmissions, this main signal remains constantly on, while the frequency or amplitude changes up or down. The radiotelegraphy method, in contrast, completely toggles the entire radio signal. Like a flashing light, the radio waves can be either completely on or completely off, but do not vary in between.
Radiotelegraphy relies on Morse code "dots and dashes" to send and receive messages. For each "dot" of the code, the signal switches on for a short moment. For a "dash," the signal switches on for a longer period of time. This method dates back to the beginning of the radio industry, and was first used by telegraph companies. Though dated, radiotelegraphy is still used today due to its advantage of transmitting a solid signal over long distances.
The radio teletypewriter method of communication works in a similar way as radiotelegraphy, but automates the coding process. Instead of relying on a human operator to input dots and dashes, electronics interpret the on-and-off pattern of the carrier wave. This allows messages to be sent at a faster rate than a human can operate, and enables messages to be received even if the teletypewriter is unmanned.
This method received its name due to the way messages are printed. As the electronics decode an incoming message, a printer imprints the proper character onto paper. This approach allows messages to be easily retrieved and shared between different people, and is commonly used on large ships where different officers must act on the same information.
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