NAB spokeswoman Ingram, said the $1.5 billion currently set aside will cover about 33 million converter boxes. But about 38 million U.S. households have at least one set that uses an antenna to receive analog transmissions.
Officials are also concerned that consumers will be caught unaware by the switch to digital or be confused about what steps they need to take.
The government has allotted $20 million to fund campaigns to educate people, and Ingram said industry groups are ramping up their own outreach programs. They plan to reach consumers through TV commercials, speeches and appearances by trucks designed to look like televisions.
But Joel Kelsey, a spokesman for Consumers Union, warned that current funding might not be enough - particularly to reach elderly and low-income viewers who will be most affected by the switch.
"It's my firm hope that the DTV transition will go swimmingly," he said. "But we should be concerned that there are some consumers that are not being reached."
A recent survey by Consumers Union found that three out of four households that would be affected by the change didn't know the converter box vouchers were available. Of the families surveyed, 42 percent said they had no plans to do anything to prepare for the change.
"Citizens and consumers didn't ask for the digital transition," Kelsey said. "It's the job of the government to help them sort out some of the noise and understand the lowest-cost path."
One point of confusion is the converter boxes themselves. EchoStar currently offers the cheapest box at $39.99, but boxes can cost upwards of $100.
Some include extra features, such as built-in DVR for recording programs for later viewing, but simpler - and cheaper - boxes will do the job.
A study released last week suggested consumers might want to beware when shopping for the boxes.
The Maryland Public Interest Research Group found that sales clerks at retail chains were misleading broadcast viewers who were trying to prepare for the transition. About half of the clerks tried to "up-sell" consumers by directing them to more expensive products.
The report found that many are confused by the digital transition and might end up buying expensive high-definition digital televisions, when all they need is a standard-definition digital set or a converter box.
Most sets purchased before 2004 were analog TVs that cannot interpret over-the-air digital signals without a converter box. Newer sets may be capable of receiving digital broadcasts without a converter box.
