http://www.latimes.com/business/la-fi-radio12jul12,1,720816.story

The Los Angeles Times site requires registration, but it's free.

To sum up the story: Clear Channel, owner of over a thousand US radio
stations, had avoided the limits on the number of broadcast
properties one company may control in a single market by leasing the
entire broadcast day on five Tijuana BC stations. Under the old
Federal Communications Commission rules, the San Diego radio market
ended at the US-MX border. Under new rules adopted this month, SD and
Tijuana are considered all one entity for radio audience measurement,
and group ownership, purposes.

The San Diego situation has always been unique among US cities: a big
city next to another big city across an international border, where
English is not the official language, but where there's always been a
handful of stations beaming their programming to a foreign country.

The tradition of MX-US cross border listening goes back to the days
of high-powered stations within sight of the Rio Grande, whose mix of
country and hillbilly music, preachers, and ads for patent medicines,
was beamed exclusively to US listeners. Then came Wolfman
jack,"infomercials" selling oldies albums by mail order, and XETRA-
FM, a pioneer modern rock station.

XEPRS, the Wolfman's old home, is now all Spanish, but XETRA's AM
sister station has aired a variety of English formats for over forty
years, and XHRM is the "jammin' oldies" station for San Diego. The
only clue that the stations are in Mexico is the Spanish legal ID
given once an hour. (Which was always part of the mystique of
listening to Mexican radio on the US side of the border: like the
kids in "American Graffiti," you never knew exactly where it was
coming from.)