RADIO

From the “You Scratch My Back . . .” File: Public radio station KCRW-FM (89.9) and commercial station KKGO-FM (105.1), which recently switched from an all-jazz format to all-classical, are embarking on an unusual venture in cross-promotion. Starting Tuesday, KCRW will air three announcements per day promoting KKGO’s classical concert service; in exchange, KKGO will advertise KCRW’s daily broadcasts of National Public Radio’s newsmagazine, “Morning Edition.” The unusual marriage between a public and a commercial radio station was inspired by a KKGO on-air promotion campaign that invites listeners to “tell a friend” about the station’s new classical music concert series.