But the two ambulance workers who had found him could not lift him or reach the Coast Guard with their cellphones or hand-held radios.
Their options dwindling, one of them used his radio to call an emergency center in town, where, he remembered, there was an amateur radio operator.
"The situation was getting pretty dire, because this guy had serious medical complications," said Mark Bort, the amateur operator who took the call and, his radio more reliable than the ambulance crew's, who notified a Coast Guard helicopter, which rescued the man.
All over Louisiana, Mississippi and Alabama, a volunteer army of nearly 1,000 amateur radio operators have stepped in to help fill the communications void that was left when Hurricane Katrina snapped telephone poles and toppled many cellphone towers. These ham operators suddenly find themselves in great demand: the Coast Guard, the American Red Cross and the Federal Emergency Management Agency have all made requests in the last week for more volunteer operators to handle communications at hospitals, evacuation centers and emergency operations facilities.
"When all else fails, they turn to us," said Gary Stratton, who is coordinating Louisiana's volunteer operators from a base at the emergency operations center in Baton Rouge. "Until phone lines are replaced and cells are no longer overwhelmed with traffic, we are the ones keeping this area connected."
In Gulfport, volunteer operators dispatched by FEMA to hospitals and evacuation shelters have been using their radios round the clock to send emergency calls.
At airports in Texas and Alabama, ham operators have been tracking evacuees and notifying the Baton Rouge operations center of their whereabouts so their families will be able to find them.
Ham operators have also helped locate the stranded in New Orleans. Although many in need of rescue there had cellphones, once the storm hit they were able to reach the authorities only by calling people outside the area, because the landlines on which 911 calls within the city depended had been destroyed.
"People elsewhere in the state who were getting panicked calls from folks in New Orleans were contacting their local 911," said David Gore, a spokesman for the Louisiana ham operators. "When those 911 operators got these calls, they passed them to volunteer ham operators that we stationed at these call centers, and that's how the information was then relayed back into New Orleans for rescue missions."
Ham operators use transmitters that can send messages to other operators both locally and around the world. Depending on the frequency and the time of day, these signals are sometimes easier to detect far away than nearby. Partly as a result, people in states as distant as California and Maine have also been helping coordinate relief efforts.
Mark Conklin was called into action last Wednesday after hearing a plea from another amateur operator, who had discovered an amputee stuck on a New Orleans bridge where her car had run out of gasoline. That operator was having trouble getting in touch with the Coast Guard locally, but his signal bounced clearly to Mr. Conklin in Tulsa, Okla., who did contact the Coast Guard. The woman was rescued.
"Tulsa just happened to be the right spot at the right time for this signal, so the message landed in my lap," said Mr. Conklin, a sales manager for an appliance store.
At her home in Shelton, Conn., Betsey Doane, who is blind, has been spending several hours a day monitoring her radio, awaiting a chance to help. One opportunity came over the weekend, after she received a message about a woman who had been stranded in her New Orleans home for close to a week. The woman's mother had been trying for days to get a call through to the New Orleans police, and it was Ms. Doane who, using her radio, was finally able to reach police officers.
"I think most of us are glad to help," she said. "It's one of the reasons we're operators."
Allen Pitts, a spokesman for the American Radio Relay League, the national association for amateur radio, said there were about 670,000 amateur operators in the nation licensed by the Federal Communications Commission.
"We remain in obscurity until disasters hit," Mr. Pitts said. "And then everyone tends to come running to us for help."