Digital television offers the promise of super-sharp pictures and better sound, and there's now a firm deadline for broadcasters to complete the transition to all-digital signals.

Legislation passed by the Senate on Wednesday would require broadcasters to end their traditional analog transmissions by Feb. 17, 2009, and send their signals digitally.

The deadline was part of a larger budget bill that narrowly passed the Senate. House approval is expected and President Bush praised the Senate vote.

The plan also would allocate as much as $1.5 billion for a "converter box" program to help people with older, analog TV sets that would lose their signals in the digital era.

Consumer advocates say that is not enough money.

"We think this is unfair, unworkable and unacceptable. It virtually ensures that on Feb. 18, 2009, tens of millions of televisions go black," said Jeannine Kenney, senior policy analyst with Consumers Union, the publisher of Consumer Reports.

The group says the fund — after subtracting operating and other costs — would cover fewer than 17 million households.

An estimated 21 million households do not get cable or satellite service and rely solely on free over-the-air TV. Consumers Union estimates an additional 20 million homes that have cable or satellite do not have all of their TV sets hooked up to the service and would need converter boxes, too.

Consumers with analog sets would be able to request two $40 coupons to help buy the set-top boxes, which are expected to cost $50 to $60 each. There is no income cap for those who may request the coupons.

GOP supporters such as the chairman of the House Energy and Commerce Committee, Rep. Joe Barton, R-Texas, have said lawmakers do not expect to subsidize wealthier homes.

People who have newer TV sets capable of receiving digital signals would not notice a change when the switch is made in 2009. Nor should satellite television viewers or the roughly 26 million households with digital cable.

Cable industry representatives say there is the potential for a service disruption for some of the 40 million cable customers without digital. If they still have analog TV sets in 2009, they could lose some stations.

For those households, cable operators would convert digital signals back to analog for the major broadcast stations. But that may not happen for smaller, independent stations unless those stations and cable operators work out a deal or Congress intervenes.

Analysts expect some agreement.

"It seems likely that Congress will plug this gap at some point before the hard date cutover," said Paul Gallant, media policy analyst at Stanford Washington Research Group.

The move to all-digital will free valuable radio spectrum, some of which has been allocated to improve radio communications among fire and police departments and other first responders.

The government would auction the rest of the spectrum for an estimated $10 billion, though private estimates put that number higher.

The bill also would provide $1 billion to upgrade public safety communications systems.

The Feb. 17, 2009, deadline was a compromise. The House initially proposed ending analog transmissions on Dec. 31, 2008; the Senate had backed April 7, 2009, after the NCAA basketball tournament.

The Senate had also initially proposed a $3 billion converter box subsidy.