In San Diego, they're bringing down the curtain on 60 years of broadcast history just before midnight tonight. 

KFMB-TV, a pioneer television station that first took to the air on May 16, 1949, will switch off its signal on Channel 8 for the last time. The station, a CBS affiliate, will pull the plug in the middle of "Late Night with David Letterman."  But KFMB-TV isn't going out of business; it's one of four San Diego stations changing from analog transmission to digital under federal rules that will free up the airwaves for other purposes.
 
All told, 421 U.S. television stations will sign off analog broadcasts tonight, affecting only viewers with who get their television on conventional receivers the old-fashioned way: over the air, through antennas.  Previously, 220 other stations in Hawaii, Wilmington, N.C. and Chico-Redding, Calif. made the changeover. Customers who subscribe to cable or satellite TV won't notice any changes at all. 

Some not prepared 
Still, the outfit that brings you the ratings, the Nielsen Co., estimates that 6.5 million homes nationwide are unprepared because they don't have newer digital sets or haven't purchased converters for their older TVs.  (In San Diego, the largest television market with the majority of stations terminating analog broadcasts tonight, it's estimated that 65,000 households receiving over-the-air TV are not ready for the transition.)
 
The government wasn't ready for the transition either.  A program to give people $40 rebate coupons for converter boxes ran out of money, leaving millions of consumers in limbo until Congress voted to allocate more funds.
 
The government also extended the deadline for a complete switchover until June 12 because of all the confusion surrounding the change. But it left a loophole for broadcasters who complained about the high cost of running analog and digital transmitters simultaneously. 
 
In many cities, the Federal Communications Commission gave broadcasters the option of switching to digital on the original changeover date of Feb. 17 as long as one major network affiliate in each of those cities kept the analog signal going until June.
 
So, in San Diego, that honor falls to KNSD, a station owned by NBC.  Across the country, all network owned-and-operated stations have agreed to a stay of execution for analog TV until the June 12 date.
 
"This is not just about whether people can watch their favorite reality show," said acting FCC Chairman Michael Copps in a written statement.  "It's about whether consumers have access to vital emergency alerts, weather, news and public affairs."

Digital limits
But will they?  In some fringe areas where the old analog signals were marginal, viewers may find that even with a digital converter, there may be no reception whatsoever or reception only on some channels.  That's because digital signals don't always travel as well as analog around obstructions like hilly terrain or tall buildings. Consumers who were able to get by on indoor "rabbit ears" antennas may now have to spring for the cost of installing more powerful rooftop antennas.
 
In San Diego, Gary Stigall, a longtime TV engineer, said he thinks the impact could be minimal because  "93 percent of the people here have cable, meaning they won't be affected."  But 7 percent of the audience is still a fairly sizeable number.
 
Tomorrow morning, the FCC plans to have call centers up and running to answer consumer questions about the transition as some people who didn't prepare for the digital TV transition wake up to blank screens on most of their old channels.  "We are trying to make the best of a difficult situation," the FCC's Copps said.
 
The number is 1888-CALL-FCC.  They're expecting plenty of public response.