World Library  
Flag as Inappropriate
Email this Article

FM broadcasting in the United States

Article Id: WHEBN0000066059
Reproduction Date:

Title: FM broadcasting in the United States  
Author: World Heritage Encyclopedia
Language: English
Subject: NBC, Progressive rock
Publisher: World Heritage Encyclopedia

FM broadcasting in the United States

FM broadcasting in the United States began in the 1930s at engineer and inventor Edwin Howard Armstrong's experimental station, W2XMN. The use of FM radio has been associated with higher sound quality in music radio.

History of FM radio in the U.S.

In the United States FM radio stations broadcast at frequencies of 87.8–107.9 MHz. FM radio was developed in the United States by Edwin Armstrong.

During the 1930 there were a small number of experimental (known as "Apex") stations attempting to broadcast high fidelity audio using wide-bandwidth AM on VHF frequencies. In 1937 W1XOJ was the first FM radio station, granted a construction permit by the FCC. On June 17, 1936, FM radio was demonstrated to the FCC for the first time.[1] On January 5, 1940, Edwin H. Armstrong demonstrated FM broadcasting in a long-distance relay network, via five stations in five States.[2][3] FM radio was assigned the 42 to 50 MHz band of the spectrum in 1940.

After [5] On March 1, 1941 W47NV began operations in Nashville, Tennessee, becoming the first modern commercial FM radio station. However, FM radio did not recover from the setback until the upsurge in high fidelity equipment in the late 1950s.

By the end of the 1970s, 50.1% of radio listeners were tuned to FM, ending AM's historical prevalence. By 1982, FM commanded 70% of the global audience and 84% among the 12-24 year old demographic.[6]

The shift in popularity of FM radio over AM in United States during the 1970s has been called by record producer Steve Greenberg "a seismic technological shift that had torn apart the very idea of the mass audience upon which pop hits depended".[6]

During the 1970s, FM radio experienced a golden age of integrity programming, with disc jockeys playing what they wanted, including album cuts not designated as "singles" and lengthy progressive rock tracks.

FM radio channel assignments in the U.S.

In the United States, frequency-modulated broadcasting stations operate in a frequency band extending from 87.8 MHz to 108.0 MHz, for a total of 20.2 MHz. It is divided into 101 channels, each 0.2 MHz wide, designated "channel 200" through "channel 300." In actual practice, no one except the FCC uses these channel numbers; the frequencies are used instead.

To receive a station, an FM receiver is tuned to the center frequency of the station's channel. The lowest and almost-unused channel, channel 200, extends from 87.8 MHz to 88.0 MHz; thus its center frequency is 87.9 MHz. Channel 201 has a center frequency of 88.1 MHz, and so on, up to channel 300, which extends from 107.8 to 108.0 MHz and has a center frequency of 107.9 MHz.

Because each channel is 0.2 MHz wide, the center frequencies of adjacent channels differ by 0.2 MHz. Because the lowest channel is centered on 87.9 MHz, the tenths digit (in MHz) of the center frequency of any FM station in the United States is always an odd number. FM audio for analog television channel 6 was formerly broadcast (until analog television broadcasts in the U.S., except for a few low-power stations, ended in 2009) at a carrier frequency of 87.75 MHz, and many radios could tune this low; a few low-power are operated solely for their right to use this frequency and broadcast only nominal video programming, if any. For the same reason, assignment restrictions between TV stations on channel 6 and nearby FM stations are stringent: there are only two stations in the United States (KSFH, a 10-watt student station, and translator K200AA) licensed to operate on 87.9 MHz, both because they were forced off of other channels. Therefore, in effect, the FM broadcast band comprises only FM channels 201 (88.1 MHz) through 300 (107.9 MHz).

Originally, FM stations in a market were generally spaced four channels (800 kHz) apart. This spacing was developed in response to problems perceived on the original FM band, mostly due to deficiencies in receiver technology of the time. With modern equipment, this is widely understood to be unnecessary, and in many countries shorter spacings are used. (See FM broadcast band.) Other spacing restrictions relate to mixing products with nearby television, air-traffic control, and two-way radio systems as well as other FM broadcast stations. The most significant such taboo restricts the allocation of stations 10.6 and 10.8 MHz apart, to protect against mixing products which will interfere with an FM receiver's standard 10.7 MHz intermediate frequency stage.

Commercial broadcasting is licensed only on channels 221 through 300 (the upper 80 channels, frequencies between 92.1 and 107.9 MHz), with 200 through 220 (the lower 21 channels, frequencies between 88.1 and 91.9 MHz) reserved for non-commercial educational (NCE) broadcasting. In some "Twin city" markets close to the Canadian or Mexican border, such as Detroit, Michigan and Windsor, Ontario, Canada, or San Diego, California and Tijuana, Baja California, Mexico, commercial stations operating from those countries target U.S. audiences on "reserved band" channels, as neither Canada nor Mexico has such a reservation. Because of this necessary sharing, the FCC reserves a few other channels for such NCE stations.

FM stations in the U.S. are now assigned based on a table of separation distance values from currently licensed stations, based on station "class" (power output, antenna height, and geographical location). These regulations (see Docket 80-90) have resulted in approximately double the number of possible stations, and increases in allowable power levels, over the original bandplan scheme described above. All powers are specified as effective radiated power (ERP), which takes into account the magnifying effect (gain) of multiple antenna elements.

FM broadcast zones in the U.S.

The U.S. is divided into Zone I (roughly the northeastern quarter of the U.S. mainland, excluding the far northern areas), Zone I-A (California south of 40 degrees latitude, U.S. Virgin Islands, Puerto Rico), and Zone II (all other locations). The highest-power stations are class C in zone II, and class B in the others. There are no B stations in zone II, nor any C stations in the others. (See the list of broadcast station classes.) Canada is also divided in this manner, based on the most highly populated regions.

High power is useful in penetrating buildings, diffracting around hills, and refracting for some distance beyond the horizon. 100,000 watt FM stations can regularly be heard up to 100 miles (160 km) away, and farther (e.g., 150 miles, 240 km) if there are no competing signals.

A few old "grandfathered" stations do not conform to these power rules. WBCT (93.7) in Grand Rapids, Michigan, runs 320,000 watts ERP, and can increase to 500,000 watts ERP by the terms of its original license. This huge power level does not usually help to increase range as much as one might expect, because VHF frequencies travel in nearly straight lines over the horizon and off into space. Nevertheless, when there were fewer FM stations competing, this station could be heard near Bloomington, Illinois, almost 300 miles (480 km) distant.

See also


  1. ^ United Press report, "Radio Set-up Eliminates All Noise," Ogden Standard-Examiner, June 18, 1936, p1
  2. ^ Staticless" Radio Receives Relay Test""", New York Times, January 6, 1940, retrieved January 19, 2010 
  3. ^ "First F-M Network Broadcast", Broadcasting, January 15, 1940, retrieved January 19, 2010 
  4. ^ Lawrence Lessing (1956). Man Of High Fidelity. J. B. Lippincott. 
  5. ^ From Fledgling to Floundering to Flourishing: A history of FM Broadcasting in Michigan from the 1930s through the 1960s
  6. ^ a b Greenberg, Steve (November 29, 2012), Michael Jackson's 'Thriller' at 30: How One Album Changed the World, Billboard, retrieved April 15, 2014 

External links

Related websites

  • An Introduction to FM MPX
  • Stereo for Dummies Many graphs that show waveforms at different points in the FM Multiplex process
  • FM Transmitters
This article was sourced from Creative Commons Attribution-ShareAlike License; additional terms may apply. World Heritage Encyclopedia content is assembled from numerous content providers, Open Access Publishing, and in compliance with The Fair Access to Science and Technology Research Act (FASTR), Wikimedia Foundation, Inc., Public Library of Science, The Encyclopedia of Life, Open Book Publishers (OBP), PubMed, U.S. National Library of Medicine, National Center for Biotechnology Information, U.S. National Library of Medicine, National Institutes of Health (NIH), U.S. Department of Health & Human Services, and, which sources content from all federal, state, local, tribal, and territorial government publication portals (.gov, .mil, .edu). Funding for and content contributors is made possible from the U.S. Congress, E-Government Act of 2002.
Crowd sourced content that is contributed to World Heritage Encyclopedia is peer reviewed and edited by our editorial staff to ensure quality scholarly research articles.
By using this site, you agree to the Terms of Use and Privacy Policy. World Heritage Encyclopedia™ is a registered trademark of the World Public Library Association, a non-profit organization.

Copyright © World Library Foundation. All rights reserved. eBooks from Project Gutenberg are sponsored by the World Library Foundation,
a 501c(4) Member's Support Non-Profit Organization, and is NOT affiliated with any governmental agency or department.