CHICAGO - Rabbit ears on a mobile phone? Well, not exactly, but American broadcasters and gadget manufacturers are working to beam live television to portable devices.

The American broadcast industry has been developing mobile digital TV for several years, and a small number of stations are on the air, but the platform’s availability remains limited.

In 2011, the technology is expected to gain momentum in the U.S. as the Mobile Content Venture, a group of 12 major broadcasters, will be upgrading stations to start delivering mobile DTV in 20 markets covering more than 40 percent of the U.S. population.

In the initial rollout, viewers in metropolitan areas are scheduled to receive at least two free channels during the second half of 2011.

"I wouldn’t say we’re at the tipping point," said John Taylor, a spokesman for LG Electronics, which helped develop the industry standard for mobile DTV. "But with the impending ramp-up of widespread availability of mobile DTV signals around the country, we anticipate that manufacturers will gear up their plans to introduce more products."

While portable television sets have been around for decades, the broadcast industry’s 2009 transition from analog to digital transmissions rendered most of those gadgets obsolete. With the advent of smart phones and widespread wireless connectivity, technology companies hope watching live TV will become part of consumers’ mobile diet.

The technical standard for the technology was formally adopted in October 2009, and about 70 stations in the U.S. will have launched mobile DTV by the end of this year, said Anne Schelle, executive director of the Open Mobile Video Coalition.

Mobile DTV piggybacks on the same digital signals that broadcasters use to beam programming to regular TVs. This means a consumer watching mobile DTV on a smart phone, for example, doesn’t have to worry about buffering or other issues that can snarl streaming video on a wireless carrier’s network.

"Because (mobile DTV) works outside of the cell phone network, it doesn’t matter if you have one person tuning in or 10 million people tuning in," said Salil Dalvi, an NBC executive who also serves as co-general manager of the Mobile Content Venture.

The platform also enables live local TV, providing an alternative to on-demand mobile video services. With mobile DTV, depending on what stations offer, viewers may be able to watch local news or sports broadcasts in real time while on the go.

Despite industry enthusiasm around mobile DTV, the platform faces several hurdles in gaining widespread adoption. The quality and variety of programming could vary significantly between stations and markets, particularly if broadcasters have trouble negotiating rights for certain kinds of content: national sporting events, for example.

On a broader level, mobile DTV may not appeal to consumers accustomed to on-demand content, said Charles Golvin, principal analyst at Forrester Research.

"Something that adopts the broadcast model is so last century ... especially (given that) new mobile technology adoption is driven by early adopters," he said. "It’s not only a mismatch to the expectations of consumers at large, but it’s a gross mismatch to the expectations of early adopters."

In a blow to the budding industry, chip-maker Qualcomm Inc. has decided to shut down Flo TV, a broadcast network service it created in 2004 for mobile phones, in the spring after failing to gain enough subscribers. At a November industry event, Qualcomm Chief Executive Paul Jacobs said that while live programming was popular, customers did not tune in at specific times to watch scheduled shows on their phones.

Dalvi believes the live and local nature of the Mobile Content Venture’s service will appeal to viewers who want to follow a breaking news event or catch a favorite program in real time when they’re not at home.

"I like to think about our service and what we do as a complement to the overall experience, not that consumers decide, ‘I’m going to get live TV instead of TV over the Internet,’ " he said.

The business model for mobile DTV providers remains a matter of debate. Dalvi said the Mobile Content Venture is going to leave "flexibility" for its members to offer premium content in the future, although the first channels they offer next year will be free and supported by advertising.

Because mobile DTV is part of the transmission broadcasters already send to homes, implementation costs are minimal, especially compared with the heavy investment made during the 2009 digital transition. But broadcasters and content providers see this emerging technology providing fresh revenue streams, and viewers may be asked to fork over more money for premium content such as expanded local sports coverage or a 24-hour kids entertainment channel.

Analysts say consumers are opposed to paying more than once for TV programming.

"If they pay to receive a package of channels from either a satellite or cable provider or telephone company, they don’t want to pay again for a mobile subscription," said Michelle Abraham, principal analyst at In-Stat.

The availability of mobile DTV-enabled devices is another crucial factor in the adoption of the technology. A gadget needs a special tuner to receive the signal. Industry players say they expect a greater number of accessories for laptops, netbooks and phones to arrive in the market next year. The technology also will show up in portable DVD players and screens made for cars that can be installed in the back of the headrest.

Eventually, mobile DTV tuners will be embedded into products such as tablets and phones, eliminating the need for an add-on antenna. At next month’s Consumer Electronics Show in Las Vegas, LG will show a prototype smart phone running the Android operating system that has a 4-inch screen and a telescopic antenna designed to receive mobile DTV transmissions, Taylor said.

The industry’s first task, however, is to overcome a "big marketing challenge" in explaining the benefits of mobile DTV to consumers, he said.

"Consumers don’t have widespread awareness or understanding of mobile DTV yet," Taylor said. "But consumers are beginning to embrace mobile video, whether it’s little clips you get on your cell phone or streaming on your computer. They understand you don’t have to just watch TV on that 42-inch plasma in the living room.

"The challenge we have is to help consumers understand ... it’s different than what comes through your cell phone. It’s live, local TV."