XEROK-AM (800 kHz) is a commercial radio station in Ciudad Juárez, Chihuahua, Mexico. It is licensed to operate with a power of 150,000 watts on a carrier frequency of 800 kHz, although its new transmitter is now powered at 50,000 watts. The station calls itself "Radio Cañón." XEROK is the dominant Class A station on 800 AM, a Mexican clear channel frequency. The station had a colorful history as a border blaster, aiming its programming at listeners in the United States, when at night, its 150,000-watt signal could be easily heard in many parts of the Southwest. History The licensing history for XEROK begins not in Ciudad Juárez but in Piedras Negras, Coahuila, away, with the authorization for XEPNA (more commonly XEPN) 660, made to the Compañia Radiodifusora de Piedras Negras (Piedras Negras Broadcasting Company). The callsign changed to XELO in 1936, authorized for 50 kW day from Piedras Negras but on 1110 kHz. It was the first station in Piedras Negras, operated by W. E. Branch and Claudio Bres Jáuregui from studios at the Hotel del Ferrocarril. The binational structure of the radio station—it earned 95 percent of its advertising revenue from American accounts—caused tax issues in the United States, where a sister company, The Radio Service Co., had been established in Eagle Pass, Texas, across the border. In Eagle Pass, it made $72,000 in advertising revenue in 1936 and $66,000 in 1937, prompting scrutiny by the Internal Revenue Service and a lawsuit that the company won. A spark in one of the transmitter facilities for XELO, knocking it off the air, would serve as a pretext for the station to relocate from Piedras Negras to Ciudad Juárez. When the station relocated to Ciudad Juárez, it moved to 800 kHz and tripled its power. The 150 kW plant was custom-built in 1940–1941 by a team led by William "Bill" Branch, an early well-known radio engineer. Branch built a series of amplifiers to get power from low power oscillator level to the 150 kW level. Modulation was achieved by Doherty modulation, which while complicated, allowed extremely high levels (exceeding 100% positive), of modulation and did not require large (and generally poor-performing 'Modulation Reactor') (ie. Tramformer)), audio coupling transformers. One of the border blaster stations aimed at American listeners, the long time format was Spanish-language programs by day and brokered time programs (very often in English) targeted to audiences in the