Across the country, stations are vying to hold on to listeners as AM radio's audience slowly dwindles. The persistent technology, long dwarfed by FM, has weathered more recent threats including satellite and Internet radio. It is also contending with a new assault from smartphones.

How long before AM radio disappears, if ever, is anybody's guess. But analysts say the fight for relevance is playing out in Los Angeles, the nation's largest radio market by revenue. And KFWB-AM (980), a station founded by movie studio mogul Sam Warner back before the golden age of radio, might be in the thick of it.

After 46 years of presenting news and talk, the veteran station of the AM dial is switching to an all-sports format to rev up its paltry ratings. The change comes after years of erosion for an institution that once was one of L.A.'s top outlets, from the early days of rock 'n' roll, when KFWB was known as "Color Radio," to the years when it had news bureaus throughout California.