First there was digital television. Now comes mobile digital TV.

Designed to let viewers watch TV on the go, mobile DTV is the network television industry's answer to a generation that's often more likely to watch YouTube on their iPhones than the TV in their living rooms.

Ever since the first U.S. broadcast occurred in 1928, TV signals largely have been limited to screens that sit still in order to tune in. This year, however, local stations across the country will start transmitting a new type of signal that can be picked up by devices that travel, including laptops, smart phones, portable DVD players and mini-tablets - all to be showcased at the Consumer Electronics Show starting Friday in Las Vegas.

"We need to follow our consumers," said Brandon Burgess, chief executive of Ion Media Networks Inc. in Manhattan, which owns 59 broadcast TV stations. "The trends are clear that mobile devices are where consumers will be getting video.

Today, a number of companies offer popular shows over portable devices, mainly cell phones. What's different about the latest offering is its price: Free.

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Instead of paying anywhere from $7 to $15 a month to subscribe to FLO TV or MobiTV, mobile DTV will be transmitted directly by local broadcasters for free, at least for now.

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About 800 TV stations covering 103 million U.S. homes are backing the effort. Other broadcasters supporting the initiative include News Corp.'s Fox Television Stations, Univision Communications, Sinclair Broadcast Group and the Corporation for Public Broadcasting, among others.

A sample of those are expected to be shown at the electronics show, including a 7-inch combination DVD player and mobile DTV from LG Electronics.

Another way to access mobile DTV will be through a wireless gadget, the Tivit, set to go on sale later this year for around $120.