Can Mel Karmazin pump up the volume at Viacom's ( VIAB) radio operations this year? That's what Wall Street is betting. Driven in part by the Viacom president's public vows to whip the radio division into shape, analysts have modeled steady improvement in the radio business's revenue and bottom-line results. But signs of strengthening radio aren't as clear as bulls might hope. And as media companies have discovered annually over the past few years, the second half of the year isn't obligated to bring the rebound that optimists expect in the first half. The grass isn't always greener on the other side of June 31. Though radio is only a slice of Viacom's operations -- it amounted to 19% of earnings before interest, taxes, depreciation and amortization last year, according to Blaylock & Partners -- the Infinity radio operations carry a hefty amount of symbolic weight among investors. Not only did the can-do Karmazin work his way to the top of the broadcasting business via radio, but he has also made numerous public statements this year that Viacom's radio is broken -- and that he will surely fix it. "The radio business is sort of Mel's baby, because that's what he grew up in," says David Joyce, an analyst at Guzman & Co. On Friday, Viacom's shares rose 3 cents to close at $45. Shares in the media and entertainment conglomerate reached a 52-week high of $49.75 late last month.