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Beginning in 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 400 meters.
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
frequencies.
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.
1926 -- 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.
APRIL 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
nations.
You can
see the impact of NARBA by looking first at
Radex March April 1940
which
has a
chart of channel changes planned. NARBA,
delayed for a year, was implemented in March
of 1942 and seen post-implementation in
Radex January 1942.
The
comparisons between the two issues show how
the present day AM band was determined.
(Thanks to
http://earlyradiohistory.us/hist-dc.htm
for the dates and data. Please see that
interesting site, too.)
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