Many radio broadcasters in the 30's moved South Of The Border to avoid Broadcasting regulations and liability. So-called Mexican "Border Blasters" were licensed commercial radio station that transmitted at very high power to the United States from various Mexican cities near the border beginning in the 1930's and continuing into the 80's. There were many such stations licensed by Mexico's Secretary of Communications and Transport (SCT) using transmitters with an output far in excess of licensed commercial stations located within the USA.  The primary reason for the high powered stations was to escape United States regulations regarding power and frequency assignments. The first border station, XED, began broadcasting from Reynosa, Tamaulipas, in 1930. Owned for a time by Houston theater owner and philanthropist Will Horwitz,

While the federal government of the United States did not particularly like them, the stations were not only allowed to flourish, but in the case of Texas one governor used the stations as a part of his election campaign. The only restriction placed upon them was a law which forbade studios in the U.S. from linking by telephone to border-blaster transmitters in Mexico. This law was introduced in the wake of John R. Brinkley's romance with fascism prior to World War II on XERA. 

As was the case between the 1930's and the 1970's, some border blaster stations in areas near larger American border cities such as San Diego are leased out by American broadcasting companies and air English-language programming targeting American audiences. The American side leases the station from the Mexican station owners/licence holders and feeds programming from their American studios to the Mexican transmitters via satellite.

Most border blaster stations today program Spanish-language programming targeted at the Mexican side of the border. Some of the Spanish language border blasters target the US side of the border, some target both.

Due to Mexican government regulations, these stations, like all radio stations in Mexico, must air the Mexican National Hour on Sunday evenings (usually 8 pm or 10 pm, depending on where the station is located) and the Mexican National Anthem at 12 midnight and 5 am each day.   In addition, they must also give station identification in Spanish. This is usually done softly or during commercial breaks so the listeners on the American side won't usually notice it.

An excellent on-line article on Border Radio has been published by the University of Texas Press.   Another good source is The Handbook of Texas online.

Mexican Border Blasters Break For The Border

"Amongst Bob Smith's (Wolfman Jack) heros were disc jockey Alan Freed, aka Moondog, and blues singer Howlin' Wolf, whose names formed the inspiration for his own alias, Wolfman."