All cable-TV systems are not created equal when it comes to an emergency.
Thursday's massive earthquake showed that some Southern California cable systems were capable of delivering signals even to customers whose electricity went off. But other cable operations were quickly impaired, if not completely crippled, by the quake.
As an emergency communications link, cable systems--which carry vital news services such as Cable News Network--are potentially more vulnerable than broadcast TV because their vast wire networks depend on booster power from electric utilities. They also depend on the stability of telephone and electric poles and underground conduits.
Thanks to back-up power, however, some systems in the hardest-hit areas continued to relay signals Thursday morning.
"We never stopped transmitting, and we know that some signals were getting through," said Alan Feldstein, general manager of Sammons Communications' 8,000-subscriber system in Whittier.
According to Feldstein, Sammons' Whittier office suffered extensive quake damage, including smashed windows and a broken water main.
But the system's transmitter, at a landfill site in Whittier, continued to operate. And, Feldstein believes, most customers continued to get cable signals thanks to battery-operated back-up generators that sustain the Sammons lines for as long as two hours in the event of a power outage.
(Unfortunately, that doesn't help if your power is out at home, since the TV will be out even if the cable is on. It is also possible to lose cable service when your home power is still on, since the system might be knocked out by the failure of a booster elsewhere along the line.)
By contrast, Choice Television's Alhambra system, with 45,000 subscribers in the San Gabriel Valley, appeared to suffer a more serious service interruption--in part because it has back-up power for only "some poles," according to Cesar Rivas, a customer service representative.
"There could be a lot of people out," Rivas said at mid-morning. "That can be attributed to power outages, and they'll stay down as long as the power is down."
In a third variation, American Cablevision's South Pasadena and San Marino system, with 5,500 subscribers, initially failed because of a Southern California Edison power outage. But by mid-morning, the cable system had restored its own service by deploying back-up generators at the base of power poles.
"Our concern was to keep the system operating for customers," said Antonio Dominguez, general manager of the system. "CNN had breaking stories right as (the quake) went on. That's the great thing about cable. We can deliver that kind of coverage."
Several cable operators said that they had "over-ride" arrangements allowing local authorities to preempt cable programming for emergency messages. But those arrangements weren't used by any of several systems contacted Thursday.
"(City authorities) didn't choose to use it," Dominguez said of the San Marino-South Pasadena system. "We went to offer them the use of our trucks. So far, they haven't used them. And they never mentioned the override."