We keep waiting for some other DJ to step center stage and challenge jazz ambassador Leigh Kamman to a full-blown battle royal, juke-joint style. Since he created The Jazz Image for Minnesota Public Radio in 1973, though, the veteran host has faced few worthy adversaries. That's because the tireless night owl, a mainstay (and frequent host) at Twin Cities' jazz events from the Dakota to the Guthrie, has been honing his chops for nearly 60 years. Spinning his first disc in 1940, Kamman spent his formative days (and nights) haunting clubs and broadcasting in Harlem, Duluth, and San Francisco, where the likes of Duke Ellington, Dizzy Gillespie, and John Coltrane were inventing music on the spot. During that time Kamman's love for big band and fascination with bop mellowed into an encyclopedic expertise, which he nourished interviewing legends such as Billie Holiday and still brings to the fore on The Jazz Image when talking to the music's aging legends or newest stars. (The show airs Saturdays from 7:00 to 10:00 p.m.) With ears always open to the young cats, and a heart never far from the old-timers, Kamman uses his leisurely paced program to seduce the novice and nourish the addict.