thousand stations in seven countries". The following chart reviews the assignments before and after March 29, 1941, including information about individual U.S. and Canadian stations, and summarizes the most significant changes: Refinements A series of modifications would follow the initial treaty, which was scheduled to expire on March 29, 1946. In early 1946, a three-year interim agreement gave Cuba expanded allocations, including the right to share five U.S., three Canadian, and two Mexican clear channel allocations, plus operate high-powered stations on some regional frequencies. The changes also resulted in the Bahamas being granted use of the 1540 kHz Clear Channel by the U.S. 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. Mexico, which had withdrawn from the conference, and Haiti, which did not participate, were to be given a chance to subscribe. (The United States and Mexico made a bilateral agreement in 1957.) This agreement formally added 540 kHz as a Clear Channel frequency, and also provided for Cuba to share six, and Jamaica two, of the U.S. clear channel allocations. Some provisions remained controversial, and this version of the treaty wasn't ratified by the United States until early 1960. In 1980, Cuba gave the required one year notification that it was withdrawing from the NARBA treaty. 1981 "Rio Agreement" The NARBA treaties have been substantially superseded by the "Regional Agreement for the Medium Frequency Broadcasting Service in Region 2" (Rio Agreement), which covers the entire Western hemisphere, and was signed at Rio de Janeiro, Brazil in 1981, taking effect on July 1, 1983 at 08:00 UTC. The interference protection criteria in the Rio Agreement are significantly different from NARBA's, and the concept of clear channel stations is eliminated. In adopting this agreement, the Bahamas and Canada declared their intent to renounce their adherence to NARBA. However, much of the structure introduced by that treaty remained intact. Additional actions On June 8, 1988 another conference held at Rio de Janeiro, this time under the auspices of the International Telecommunication Union, adopted provisions effective July 1, 1990 to add ten AM band frequencies within