MADRID — Low-cost digital terrestrial TV has become an ace card for Spain’s second-biggest broadcasting conglom, Antena 3-La Sexta, driving share, priming U.S. hits and bulwarking its bottom line.

Since the merger of Antena 3 and La Sexta in March, the group’s five free-to-air DTT channels have grabbed a collective 8.5% share of the audience. One of these, femme-skewed Nova, was the fastest-growing channel in Spain, growing share from 1.3% in January to 2% in December.

The rise of free-to-air DTT channels in Spain helps explain the shift from high-cost local production to far lower-cost U.S. program acquisition in the territory.

As Spain’s TV ad market nearly halved from 2007’s Euros3.5 billion ($4.5 billion) to around $2.4 billion last year, Antena 3 has been forced to put on the back-burner production of in-house fiction hits for young-adult DTT channel Neox, such as relationship sitcom “Impares” and comedy sketch show “Coconut Museum.”

Neox, which airs U.S. skeins “Modern Family,” “The Big Bang Theory” and “Two and a Half Men,” is Spain’s third biggest channel in 13-24 demos, punching 10% 13-24 share, ahead of pubcaster TVE 1, Cuatro and La Sexta, said Bernd Reichart, outgoing Antena 3 managing director, digital channels.

“The crisis has increased grid-time for bought-in product,” added Reichart, who will serve as CEO of German channel Vox from Feb. 1. “Eight or nine years ago, we only partially tracked Hollywood. With a family of seven different channels, no major studio product can be discounted as unsuitable.”

Neox’s youth profile was “absolutely fitting” for U.S. premium product, Reichart added. “‘Two and a Half Men’ has jumped from channel to channel. Now it has a second chance to be a hit.”

“In the past, if big Spanish channels had tried to air ‘Modern Family’ in primetime, it would never have hit 15% share, and would have flopped,” one analyst said.

“Now, if ‘Modern Family’ hits 2%, it’s a success and TV networks pay for just a 2% share.”

An eight-channel spread that includes La Sexta 3 (1.6% share), driven by Warner Bros. movies, also appeals to advertisers, offering a wide range and precise demo-targeting channels, the analyst added.

DTT channel growth — up from 2.6% of free-to-air audiences in 2007 to 28.5% last year — is natural.

“With Spain’s digital switch-over in April 2010, Spaniards were forced to watch either DTT or pay TV. With the crisis, more people are watching DTT,” the analyst said.

“Mediaset Espana and Antena 3 have also added channels, increasing choice, and consumption,” he added.

Last year, average Spanish TV viewing reached a historic record of 246 minutes a day.