General Order 40

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The Federal Radio Commission's (FRC) General Order 40, dated August 30, 1928, described the standards for a sweeping reorganization of radio broadcasting in the United States. This order grouped the AM radio band transmitting frequencies into three main categories, which became known as Clear Channel, Regional, and Local. It also included provisions for coordination with Canadian station assignments. The majority of the reassignments resulting from the plan's implementation went into effect on November 11, 1928.


Radio transmissions in the United States were originally regulated by the Department of Commerce, as authorized by the Radio Act of 1912. The first formal regulations governing broadcasts intended for the general public were adopted effective December 1, 1921. This initially established just two transmitting wavelengths — 360 meters (833 kHz) for "entertainment" broadcasts, and 485 meters (619 kHz) for "market news and weather reports".[1] The number of broadcasting stations grew dramatically in 1922, reaching over 500 by the end of the year, and the government began making available additional frequencies. By November 1924 a band of frequencies, from 550 to 1500 kHz, had been established, with higher-powered stations, known as "Class B", assigned to the frequencies from 550 to 1070, while lower-powered "Class A" stations were assigned to 1080 to 1500.[2]

In 1926, the government's regulatory authority under the 1912 Radio Act was successfully challenged, and, for a chaotic period that lasted until early 1927, radio stations were free to use any frequency and power they chose, while the number of stations increased to 732. The Radio Act of 1927 was passed to regain control of the situation. The Act established a Federal Radio Commission, which reduced the number of stations, primarily through its General Order 32, in addition to eliminating "temporary" and "portable" stations. The Commission also reallocated frequency assignments to reduce interference and provide better service to smaller communities and underserved rural areas. A constraint was the Davis Amendment, which specified that the station assignments had to be equitably made throughout the country.

Two technical issues limited the number of stations that could operate without interfering with each other. These issues were especially important at night, when a change in the ionosphere meant that radio signals traveled much greater distances. Most transmitters at this time were unable to precisely control their output frequencies, thus, signals from two stations operating on the same nominal frequency would combine to make a high-pitched "heterodyne" tone that interfered with the reception of both stations. Secondly, directional antennas would not be developed until the early 1930s,[3] so there was no effective method for limiting signals in a given direction.

General Order 40 provisions[edit]

Five U.S. zones used to help ensure stations were equally allocated as required by the Davis Amendment

On August 30, 1928, the Commission issued General Order 40, which set new standards for radio broadcasting. A "broadcast band" was defined, consisting of 96 frequencies, spaced every 10 kilohertz, from 550 to 1500 kHz. Six of them—690, 730, 840, 910, 960, and 1030—were restricted for use only by Canadian stations, leaving 90 available for US assignment. The country was further divided into five zones, to coordinate the Davis Amendment directive of an equitable assignment of stations.[4]

Clear channels[edit]

Forty of the U.S. frequencies—eight in each zone—which came to be known as "Clear Channels", were generally limited nationally to a single station. The maximum power for these stations was to be determined later, and in most cases was set at 50,000 watts. In some cases, secondary stations were assigned the same frequency, with provisions to avoid interference with the primary station's coverage by locating the secondary stations long distances from the primary stations, limiting their power, or restricting them to daytime-only operation.

Due to a lack of Clear Channel frequencies, in several cases two stations were assigned the same frequency and required to share time on them:

  • 770 KFAB in Lincoln, Nebraska and WBBM in Chicago, Illinois. To avoid interference, at night KFAB carried the same network programming as WBBM and the stations closely synchronized their transmissions.
  • 820 WFAA in Dallas, Texas and WBAP in Fort Worth, Texas. Eventually, these stations also shared a second, regional frequency (570), and until 1970 alternated between the two frequencies every 12 hours.
  • 850 KWKH in Shreveport, Louisiana and WWL in New Orleans, Louisiana.
  • 870 WLS and WENR, both in Chicago, Illinois. This continued until 1959 when ABC purchased both stations and WENR was deleted.
  • 1000 WHO in Des Moines, Iowa and WOC in Davenport, Iowa. Both stations unsuccessfully fought the shared allocation. Initially the two stations transmitted the same programs using synchronized transmitters, but eventually WHO bought out WOC and consolidated operations as WHO-WOC in Des Moines. Still later WOC was split-off, leaving just WHO.
  • 1060 WBAL in Baltimore, Maryland and WTIC in Hartford, Connecticut.
  • 1160 WOWO in Fort Wayne, Indiana and WWVA in Wheeling, West Virginia.

Zone 5 Clear Channel frequency 790 kHz was assigned to General Electric's (GE) KGO in Oakland, California. Because of the separation between the stations, GE's WGY in Schenectady, New York was also assigned this frequency, but with KGO's power limited to 7,500 watts, until a directional antenna became feasible and KGO's power could be raised to 50,000 watts. KGO is the General Order 40 station on 790/810 kHz, not WGY.

Zone 2 Clear Channel frequency 1020 kHz was initially used by a high-powered station in Zone 4, KYW in Chicago, Illinois. This discrepancy was resolved when KYW moved to Philadelphia in 1934, and the Philadelphia station previously on 1020, WRAX, moved to regional frequency 920 kHz, sharing time with WPEN.

Regional frequencies[edit]

Forty-four frequencies, later known as "Regional", were designated to be used concurrently by stations in multiple zones. Forty of these frequencies had power limits of 1,000 watts, while the remaining four, 1460-1490, referred to as "Super Regional", had 5,000-watt limits. In numerous cases up to four stations in a given location were assigned the same frequency, requiring them to establish time-sharing agreements.

Local frequencies[edit]

The remaining six frequencies—1200, 1210, 1310, 1370, 1420 and 1500—later known as "Local", were issued to stations in all five zones, with a power limit of 100 watts.


The reorganization greatly reduced interference caused by the chaos that resulted from the earlier collapse of regulation. There was some controversy that the assignments had created groups of "have" and "have-not" stations—with the Clear Channel stations receiving a major economic boost, while many remaining stations, often with limited hours due to time-sharing, had constricted futures. Also, although the reorganization accounted for Canada, it did not include other nearby countries, most notably Mexico. Twelve years later this omission was addressed by the North American Regional Broadcasting Agreement (NARBA), which took effect March 29, 1941.

November 11, 1928 assignments[edit]

General Order 40's implementation took effect at 3 a.m. Eastern time on November 11, 1928, and required most U.S. radio stations to move to a new broadcast frequency.[5] A survey conducted by Radio Retailing magazine concluded that, despite some continuing issues, the changes meant that "on the whole, the broadcasting situation has been much improved".[6]

The table below presents a general outline of the allocations made under the order. For "Clear" frequencies, the zone of that frequency's principal station is listed, followed by the principal station's call letters and location, then the frequency that had been previously used by the principal station, and any additional stations assigned to that frequency. Bolded stations' call signs are the original primary assignments, while call signs shown in parentheses were owned by the same licensee as the principal station. The additional stations on a frequency were: 1) shared allocations, 2) daytimers, or 3) secondary stations which eventually achieved full-time status, but at lower power or using a directional antenna that protected the primary station's coverage.

Used for Max.
Zone Principal station(s) Other stations sharing
frequency (zone)
Calls, City Prev.
550  Regional 1,000   7 U.S. stations
560  Regional 1,000   10 U.S. stations
570  Regional 1,000   11 U.S. stations
580  Regional 1,000   6 U.S. stations
8 Canadian stations
590  Regional 1,000   5 U.S. stations
600  Regional 1,000   7 U.S. stations
3 Canadian stations
610  Regional 1,000   5 U.S. stations
620  Regional 1,000   6 U.S. stations
630  Regional 1,000   4 U.S stations
3 Canadian stations
640  Clear TBD 5 KFI, Los Angeles, California 640  WOI, Ames, Iowa (4)
WAIU, Columbus, Ohio (2)
650  Clear TBD 3 WSM, Nashville, Tennessee 890  KPCB, Seattle, Washington (5)
660  Clear TBD 1 WEAF, New York, New York 610  WAAW, Omaha, Nebraska (4)
670  Clear TBD 4 WMAQ, Chicago, Illinois 670  none
680  Clear TBD 5 KPO, San Francisco, California 710  KFEQ, Saint Joseph, Missouri (4)
WPTF, Raleigh, North Carolina (3)
690  Clear Canada CJCJ, Calgary, Alberta
NAA, Arlington, Virginia (2)
700  Clear TBD 2 WLW, Cincinnati, Ohio 700  none
710  Clear TBD 1 WOR, New York, New York (Newark, New Jersey) 710  KMPC, Los Angeles, California (5)
720  Clear TBD 4 WGN/(WLIB), Chicago, Illinois 720  none
730  Clear Canada CKAC, Montreal, Quebec CKWX, Vancouver, British Columbia
740  Clear TBD 3 WSB, Atlanta, Georgia 630  KMMJ, Clay Center, Nebraska (4)
750  Clear TBD 2 WJR, Detroit, Michigan 680  none
760  Clear TBD 1 WJZ, New York, New York (Newark, New Jersey) 660  WEW, Saint Louis, Missouri (4)
KVI, Tacoma, Washington (5)
770  Clear TBD 4 WBBM/(WJBT), Chicago, Illinois 770  none
KFAB, Lincoln, Nebraska 940 
780  Regional 1,000   6 U.S. stations
3 Canadian stations
790  Clear TBD 5 KGO, San Francisco, California (Oakland) 790  WGY, Schenectady, New York (1)
800  Clear TBD 3 WFAA, Dallas, Texas 550  none
WBAP, Fort Worth, Texas 600 
810  Clear TBD 4 WCCO, Minneapolis, Minnesota 740  WPCH, New York, New York (1)
820  Clear TBD 2 WHAS, Louisville, Kentucky 930  none
830  Clear TBD 5 KOA, Denver, Colorado 920  WRUF, Gainesville, Florida (3)
WHDH, Boston, Massachusetts (1)
840  Clear Canada CFCA/CNRT, Toronto, Ontario
850  Clear TBD 3 WWL, New Orleans, Louisiana 1220  none
KWKH, Shreveport, Louisiana 760 
860  Clear TBD 1 WABC/(WBOQ), New York, New York 970  WHB, Kansas City, Missouri (4)
KMO, Tacoma, Washington (5)
870  Clear TBD 4 WLS, Chicago, Illinois 870  none
WENR/(WBCN), Chicago, Illinois 1040 
880  Regional 1,000   7 U.S. stations
7 Canadian stations
890  Regional 1,000   9 U.S. stations
900  Regional 1,000   7 U.S. stations
910  Clear Canada CFCF/CHYC, Montreal, Quebec CKY, Winnipeg, Manitoba
CJAT, Trail, British Columbia
920  Regional 1,000   6 U.S. stations
930  Regional 1,000   8 U.S. stations
5 Canadian stations
940  Regional 1,000   6 U.S. stations
950  Regional 1,000   4 U.S. stations
960  Clear Canada CFRB/CKGW, Toronto, Ontario CFRN, Edmonton, Alberta
970  Clear TBD 5 KJR, Seattle, Washington 970  WCFL, Chicago, Illinois (4)
980  Clear TBD 2 KDKA, Pittsburgh, Pennsylvania 960  none
990  Clear TBD 1 WBZ, Springfield, Massachusetts / WBZA, Boston 910  none
1000  Clear TBD 4 WHO, Des Moines 560  KFVD, Los Angeles, California (5)
WOC, Davenport, Iowa 800 
1010  Regional 1,000   7 U.S. stations
2 Canadian stations
1020  Clear TBD 2 KYW/(KFKX), Chicago, Illinois (4) 570  WRAX, Philadelphia, Pennsylvania (2)
1030  Clear Canada CFCF, Montreal, Quebec CNRV, Vancouver, British Columbia
1040  Clear TBD 3 KRLD, Dallas, Texas 650  KTHS, Hot Springs, Arkansas (3)
WKAR, East Lansing, Michigan (2)
1470  WKEN, Kenmore, New York (1)
1050  Clear TBD 5 KNX, Los Angeles, California 890  KFKB, Milford, Kansas (4)
1060  Clear TBD 1 WTIC, Hartford, Connecticut 560  WJAG, Norfolk, Nebraska (3)
KWJJ, Portland, Oregon (5)
WBAL, Baltimore, Maryland 1050 
1070  Clear TBD 2 WTAM/(WEAR), Cleveland, Ohio 750  KJBS, San Francisco, California (5)
WCAZ, Carthage, Illinois/
WDZ, Tuscola, Illinois (4)
1080  Clear TBD 3 WBT, Charlotte, North Carolina 1160  WMBI / WCBD, Chicago, Illinois (4)
1090  Clear TBD 4 KMOX, Saint Louis, Missouri 1000  none
1100  Clear TBD 1 WLWL, New York, New York 810  KGDM, Stockton, California (5)
WPG, Atlantic City, New Jersey 1100 
1110  Clear TBD 2 WRVA, Richmond, Virginia 1180  KSOO, Sioux Falls, South Dakota (4)
1120  Regional 1,000   10 U.S. stations
4 Canadian stations
1130  Clear TBD 5 KSL, Salt Lake City, Utah 990  WJJD, Chicago, Illinois (4)
WOV, New York, New York (1)
WMAK, Buffalo, New York
1140  Clear TBD 3 WAPI, Birmingham, Alabama 880  none
KVOO, Tulsa, Oklahoma 860 
1150  Clear TBD 1 WHAM, Rochester, New York 1070  none
1160  Clear TBD 4 WOWO, Fort Wayne, Indiana 1310  none
WWVA, Wheeling, West Virginia (2) 580 
1170  Clear TBD 2 WCAU, Philadelphia, Pennsylvania 1150  KTNT, Muscatine, Iowa (4)
1180  Clear TBD 5 KEX, Portland, Oregon 1080  WDGY/WHDI, Minneapolis, Minnesota (4)
KOB, Albuquerque, New Mexico 760 
1190  Clear TBD 3 WOAI, San Antonio, Texas 1070  WICC, Bridgeport, Connecticut (1)
1200  Local 100   48 U.S. stations
1210  Local 100   44 U.S. stations
5 Canadian stations
1220  Regional 1,000   6 U.S. stations
1230  Regional 1,000   8 U.S. stations
1240  Regional 1.000   3 U.S. stations
1250  Regional 1,000   12 U.S. stations
1260  Regional 1,000   6 U.S. stations
1270  Regional 1,000   10 U.S. stations
1280  Regional 1,000   6 U.S. stations
1290  Regional 1,000   7 U.S. stations
1300  Regional 1,000   12 U.S. stations
1310  Local 100   53 U.S. stations
1320  Regional 1,000   6 U.S. stations
1330  Regional 1,000   5 U.S. stations
1340  Regional 1,000   4 U.S. stations
1350  Regional 1,000   5 U.S. stations
1360  Regional 1,000   8 U.S. stations
1370  Local 100   42 U.S. stations
1380  Regional 1,000   4 U.S. stations
1390  Regional 1,000   4 U.S. stations
1400  Regional 1,000   9 U.S. stations
1410  Regional 1,000   11 U.S. stations
1420  Local 100   38 U.S. stations
1430  Regional 1,000   7 U.S. stations
1440  Regional 1,000   9 U.S. stations
1450  Regional 1,000   9 U.S. stations
1460  Super
5,000   2 WJSV, Washington, D.C. 1480 none
4 KSTP, Saint Paul, Minnesota 1360
1470  Super
5,000   3 WLAC/WTNT, Nashville, Tennessee 1330 none
5 KGA, Spokane, Washington 1150
1480  Super
5,000   1 WKBW, Buffalo, New York 1380 none 
3 KFJF, Oklahoma City, Oklahoma 1100
1490  Super
5,000   1 WFBL, Syracuse, New York 1160 none
2 WCKY, Cincinnati, Ohio (Covington, Kentucky) none
4 WHT/WORD/WJAZ, Chicago, Illinois var.
1500  Local 100   31 U.S. stations

See also[edit]


  1. ^ "Amendments to Regulations", Radio Service Bulletin, January 3, 1922, page 10.
  2. ^ "Subcommittee No. 2: Allocation of Frequencies or Wave Lengths to Broadcasting Stations", Recommendations for Regulation of Radio adopted by the Third National Radio Conference, October 6-10, 1924, pages 16-17.
  3. ^ "History of the Directional Antenna in the Standard Broadcast Band for Purpose of Protecting Service Area of Distant Stations" by Raymond M. Wilmotte, IRE Transactions on Broadcast Transmission Systems, (Volume: PGBTS-7, Issue: 1), February 1957, pages 51-55.
  4. ^ "General Order No. 40" (August 30, 1928), Radio Service Bulletin, August 31, 1928, pages 9-10. The Davis Amendment was repealed in 1936.
  5. ^ "Revised list of broadcasting stations, by frequencies, effective 3 a. m., November 11, 1928, eastern standard time", Second Annual Report of the Federal Radio Commission for the Year Ended June 30, 1928, Together With Supplemental Report for the Period From July 1, 1928 to September 30, 1928, pages 200-214.
  6. ^ "Reallocations Improve Reception", Radio Retailing, December 1928, pages 46-47.

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