WASHINGTON - The Senate moved the digital TV transition one step closer to reality on Thursday, setting a firm date for television broadcasters to switch to all-digital transmissions.Lawmakers gave broadcasters until April 7, 2009, to end their traditional analog transmissions. The so-called "hard date" was included in a sweeping budget bill.The bill also would provide $3 billion to help millions of Americans buy digital-to-analog converter boxes for their older television sets — so those consumers will continue to receive a signal once the switch is made permanent.