1912, radio was regulated by the Bureau of
Navigation of the Department of Commerce.
Then, In December, 1921 the Commerce
Department formally established a broadcast
service, with 360 meters (833 kilohertz) set
aside for entertainment broadcasts, and 485
meters (619 khz) designated for official
government market and weather reports. The
single entertainment wavelength meant that
stations were supposed to negotiate
timesharing agreements, to keep from
interfering with each other.
In late September of 1922 a second
entertainment wavelength of 400 meters (750
kHz) was assigned for better quality, higher
powered stations. Stations on the new
wavelength were designated "Class B"
outlets, while those on 360 became known as
"Class A" stations. About thirty stations
nationwide would eventually qualify to use
On May 15, 1923 the
broadcasting service was greatly expanded,
with the designation of a band of
frequencies, in 10 kilohertz steps, from 550
to 1350 kilohertz. 550 to 1040 were set
aside for Class B stations. Class A stations
were assigned to frequencies from 1050 to
1350 khz, although existing stations were
permitted to stay at 360 meters, as "Class
C" stations. In November, 1924 the upper end
of the broadcast band was extended from 1350
to 1500 khz, providing 15 additional Class A
Until mid-1922 new
broadcast stations received three-letter
calls. After that, the Commerce Department
generally assigned Eastern stations
four-letter calls with first "A" and then
"B" as the third letter. Later stations
generally received specially requested
calls, normally four-letter, although a
few, got three-letter ones.
Commerce Secretary Herbert Hoover knew his
authority to regulate broadcasting was shaky
under the 1912 Act, but despite his pleas
Congress never acted to strengthen his
powers. Finally, adverse legal opinions
stripped away his regulatory authority.
Scores of new stations took to the airwaves
or jumped to frequencies of their own
choosing. Chaos was reported nationwide. The
Radex for October 1926
shows what the state of
the band was like; but it would not be until
the full reallocation of stations 18 months
later that some order came to the AM band.
27, 1927 -- The Federal Radio Commission,
newly created by Congress to straighten out
the broadcasting mess, began a
year-and-a-half long process to reassign
stations to non-interfering dial positions.
Radex from 1927
shows some initial reordering of the band.
NOVEMBER 11, 1928 -- The FRC finally
implemented a nationwide reassignment of
station frequencies, with stations now
classified as Local, Regional, and Clear
Channel. See the
Radex for October 1928
which shows change in
frequencies by FRC in 1928 before and after,
November 1928 and December 1928.
MARCH 29, 1941 - In conjunction with the
expansion of the broadcast band to 1600 khz,
a major frequency reallocation was
implemented nationwide. This change was a
coordinated effort of the US, Canada,
Mexico, Cuba and several other Caribbean
see the impact of NARBA by looking first at
has a chart of channel changes
planned. NARBA, delayed for a year, was
implemented in March of 1942 and seen
Radex January 1942.
comparisons between the two issues show how
the present day AM band was determined.
the dates and data. Please see that
interesting site, too.)