If you think ''Delta blues'' refers only to the music of Mississippi, you're missing part of the story. True, it was in Clarksdale, Miss., at the crossroads of Highways 49 and 61, that Robert Johnson is reputed to have sold his soul to the devil in return for his genius as a blue guitarist. But I turned north at Clarksdale and crossed the Mississippi River into Helena, Ark. That's where I found the rest of the story, still being told on a radio show that has been on the air since 1941.

The King Biscuit Time radio show is broadcast weekdays from the Delta Cultural Center in Helena, where Johnson spent much of his time. The center contains a permanent exhibit on the Delta blues and pays homage to Johnson, as well as Sonny Boy Williamson, Robert Nighthawk, Robert Lockwood Jr., and others.

King Biscuit Time has been sponsoring a blues festival for more than 20 years. It has grown into a four-day event that in some years has drawn 100,000 people to Helena, a small, poor city that is one of the bluesiest stops in the Delta.

Sonny Payne, who's in his 80s, has been hosting King Biscuit Time since 1950. The show is broadcast on KFFA-AM 1360 in Helena, but you can also hear it on the Internet, at www.kingbiscuittime.com. On the day I visited, we chatted for a few minutes as he got ready for the show. On the air a few minutes later, he announced: ''This is program number 15,554 of the original King Biscuit Time,'' then the music of Sonny Boy Williamson took over.

This is one in a series of postcards by Marjie Lambert, assistant Travel editor, who has been to all 50 states. Read her other postcards at www.MiamiHerald.com/ travel.