North American Regional Broadcasting Agreement

The North American Regional Broadcasting Agreement (NARBA, French: Accord régional sur la radiodiffusion en Amérique du Nord; Spanish: Convenio Regional Norteamericano de Radiodifusión) refers to a series of international treaties that defined technical standards for AM band (mediumwave) radio stations.

The initial NARBA bandplan, also known as the "Havana Treaty", was signed by the United States, Canada, Mexico, Cuba, the Dominican Republic, and Haiti on December 13, 1937, and took effect March 29, 1941.

Organized AM (mediumwave) radio broadcasting began in the early 1920s,[1] and the United States soon dominated the North American airwaves, with more than 500 stations by the end of 1922.

Due to a change in the ionosphere after the sun sets, nighttime signals from AM band stations are reflected for distances extending for hundreds of kilometers.

In an effort to rationalize assignments, a major reallocation went into force in the U.S. on November 11, 1928, following the standards set by the Federal Radio Commission's (FRC) General Order 40.

[5] As other countries, especially Mexico and Cuba, developed their own radio broadcasting services, the need arose to standardize engineering practices, reduce interference, and more fairly distribute clear channel assignments.

[15] Reflecting the existence of improved radio design, the Agreement also reduced the "same market" minimum frequency separation from 50 to 40 kHz.

[12] According to the Agreement's provisions, its implementation was to take place within one year after its adoption by the pact's four main signatories — the United States, Canada, Cuba and Mexico.

An engineering conference, with representatives from the U.S., Canada, Cuba, the Dominican Republic and Mexico, was held from January 14–30, 1941 in Washington, D.C., in order to coordinate the upcoming changes.

The changes also resulted in the Bahamas being granted use of the 1540 kHz clear channel by the U.S.[23] The interim agreement expired on March 29, 1949, and there was great difficulty in agreeing on a replacement, in particular due to Mexican objections, which led to two failed conferences.

A new NARBA agreement, to be effective for five years after ratification, was finally signed at Washington, D.C., on November 15, 1950, for the Bahamas, Canada, Cuba, the Dominican Republic, Jamaica and the United States.

The interference protection criteria in the Rio Agreement are significantly different from NARBA's, and the concept of clear channel stations is eliminated.