Both WSCR, the radio home of the White Sox, and WJMK are CBS Radio properties. The simulcast means WSCR fans who have access to an HD radio receiver will be able to hear the station's programming with a much higher quality sound than that now available on the AM frequency.

But sources familiar with developments think the move to add an HD frequency at WSCR could be the first step toward a full-blown simulcast of WSCR on WJMK. In October 2007, CBS Radio made a similar move in Detroit, where its AM sports outlet is now simulcast on an FM frequency.

Such a move at WSCR would likely have the immediate effect of boosting the station's ratings, which have been languishing. The addition of the HD simulcast, by itself, is not expected to substantively affect WSCR's ratings.

Though Chicago is a sports market second to none, in the April Arbitron ratings book, WSCR pulled a 1.8 rating Monday through Sunday -- good enough for only 26th place in the market in the key 25- to 54-year-old demographic. The numbers were disappointing, even though the April book included the first full month of White Sox broadcasts.