The BDR

The
Broadcasters' Desktop Resource

... edited by Barry Mishkind - the Eclectic Engineer    


The Great Frequency Change of 1941

At 3AM EST on March 29, 1941, something amazing happened as AM radio stations 
all over America changed frequency. It was planned months in advance, and was 
referred to as "Moving Day."
Not one or two at a time. Most all of them. On one day. In fact, 802 of the 893 AM 
stations in the USA changed on that night from one spot on the dial to another. 
NARBA 
What was the reason for this? It was the NARBA (North American Radio Broadcast 
Agreement). Negotiated among the US, Canada, Mexico, Cuba, the Dominican 
Republic and Haiti, this agreement was the result of four years of negotiations, from
1937 to 1941
At that time, with the increase in broadcasting stations in the US and other countries, 
more and more signals were beginning to interfere. One of the big problems in the 
1930s had been the growth of high power stations in Mexico that were aimed at the USA 
(such "bootleg" stations were outlawed under NARBA).

The goal of the NARBA was to coordinate the assignment of radio frequencies and 
minimize interference, especially between countries. 

The PLAN
Wherever it was possible, stations were left where they were, or moved to adjacent 
channels. This minimized the financial burden on the stations, who wouldn't have 
to make major adjustments to transmitters, tuning networks and antennae. 
However, the new assignment of "Clear Channels" to Canada, Mexico, and Cuba 
required some moves as far as 40 kHz up the dial.
A big "win" for broadcasters was the extension of the Broadcast Band to 540 kHz on
the low side to an extra 100 kHz, the top was now 1600 kHz. Channels set aside for 
local stations were 1230, 1240, 1340, 1400, 1450, and 1490 kHz. 
In general, here is how the negotiators designed the moves:

 91 stations from  550 kHz to  720 kHz were left unchanged. 
 21 stations from  740 kHz to  780 kHz were moved up 10 kHz.
 22 stations from  790 kHz to  870 kHz were moved up 20 kHz.
633 stations from  880 kHz to 1450 kHz were moved up 30 kHz.
 11 stations from  880 kHz to 1450 kHz were moved up 40 kHz.
 11 stations from 1460 kHz to 1490 kHz were moved up 40 kHz.			
 63 stations on   1500 kHz             were moved down 10 kHz.
 41 stations 			       were moved in other ways.


Here are some examples of the moves made by noted United States stations:

                          Previously      New

	     WWL      850          870
	     WLS       870          890
	     WJZ       760          770  (now: WABC)
                WABC    860          880  (now: WCBS)
                WFLA     940          970   
	     WINS    1180         1000  (later to 1010)
	     WQXR   1550         1560  (now: WQEW)
NARBA was the controlling agreement between nations in the Western Hemisphere until
1981 when a Regional Agreement for the Medium Frequency Broadcasting Service in Region 2 was put into operation.

 

 

 

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