1
CHAPTER 4 / AUDIO MEDIA: MUSIC RECORDINGS, RADIO 117 ▲ t What Is Broadcasting? e term broadcast was used much earlier than the development of radio or television broadcasting as we know them today, as far back as 1883. e term “broadcasting” was borrowed from agriculture, where it referred to a form of planting seeds by casting them widely in a field rather than depositing them one at a time. In its early days, wireless communications, which was initially only radio, provided point-to-point communication where telegraph lines were impractical or unreliable. e main purpose early wireless inventors saw was ship-to-ship communications or ship-to-shore communications, which would allow ships to communicate emergencies quickly to others. Sub- sequently, radio technology was developed to permit the broad- casting of messages through wireless means to multiple locations to distribute information widely. e subsequent development of television broadcasting dozens of years later offered the oppor- tunity to transmit moving pictures as well as audio via wireless technology. Whether it is radio or television, however, broadcasting works essentially the same way. A transmitter sends messages over a part of the electromagnetic spectrum to a receiver, or antenna, which translates the message to a device such as a radio or television. e electromagnetic waves, whether they are audio or images, are then decoded by the receiving device so they can be heard or seen. CONVERGENCE CONTEXT The Alphabet Soup of Spectrum Allocation S ince the electromagnetic spectrum used for wireless communications is a limited resource, the FCC allocates various portions of it to dif- ferent uses so these applications do not interfere with each other. Electromagnetic waves are divided into cycles per second, or hertz. If a radio station is at 99.5 on the radio tuner, this means its transmitter is oscil- lating at 99,500,000 cycles per second, or 99.5 mega- hertz (MHz). “AM” stands for amplitude modulation and re- fers to how the audio signal is encoded on the carrier frequency. AM radio broadcasts between 535 kilo- hertz (kHz) and 1,700 kHz (1.7 MHz), and was the only radio signal to reach the public for a number of years. “FM” stands for frequency modulation; this re- fers to the modulation of the length of the wave. FM radio broadcasts in the 88–108 megahertz (MHz) por- tion of the radio spectrum. This band is used exclu- sively for FM radio. Other portions of the wireless bandwidth spec- trum are used for other applications, such as Global Positioning System (GPS), a system of satellites that provide location information anywhere in the world, between 1,227 and 1,575 MHz. Citizens band, or CB, radio (26.96 to 27.41 MHz) enjoyed short-lived popu- larity among the public in the 1970s and is still com- monly used by long-haul truckers today. It was also the spectrum used by Sputnik, the first satellite ever launched into space. WEB LINK How Stuff Works electronics.howstuffworks.com/radio3.htm WEB LINK U.S. Frequency Allocation Chart www.ntia.doc.gov/osmhome/allochrt.html Early radios were often built to fit in with other living room furniture.
