WQSR

For the station on 105.7 formerly known as WQSR, see WJZ-FM

The station signed for the first time in 1947 as WCAO-FM, sister to WCAO (600 AM). WCAO-FM originally simulcast WCAO, but by the late 1960s/early 1970s, WCAO-FM had switched to its own classical music format.

By 1977, the station was sold to Plough Broadcasting and became WXYV V103, the major FM rival to both WWIN and WEBB (now WQLL). Originally an automated Disco format, WXYV eventually evolved into an Urban Contemporary format by the early 1980s, and by the late 1980s and early 1990s, it was Baltimore's top rated radio station. By 1995, WXYV and then-sister station WCAO were sold to Granum Communications. The following year, the stations were sold again to Infinity Broadcasting, becoming a sister station to Hot AC-formatted WWMX, Mix 106.5. (WCAO would later be sold to Clear Channel Communications (now iHeartMedia), and eventually become a sister station to WQSR.)

On June 20, 1997, at Noon, after having lost a large number of listeners to urban powerhouse WERQ, the station became Top 40 102.7 XYV. The final song on V103 was "It's So Hard to Say Goodbye to Yesterday" by Boyz II Men, while the first song on 102.7 XYV was "Be My Lover" by La Bouche.[3][4] The new format started with a dance lean, before repositioning to a hip-hop lean, and then alternative; this was done in search of an audience. The station changed branding to B102.7 on August 7, 1998, and would shift their playlist to a more mainstream direction the following year.[5] WXYV and WWMX would "compete" against each other due to the similarity of the Top 40 and Hot AC formats, despite being sister stations. While WXYV had higher ratings than WWMX, the latter station had better advertising revenue, so WXYV was chosen to flip to end the competition.

On September 8, 2001, at 6 a.m., after playing "It's So Hard to Say Goodbye to Yesterday" by Boyz II Men, WQSR and its oldies format moved over from 105.7 to 102.7. (WQSR programming was simulcast on both 102.7 and 105.7 to direct listeners to the new frequency.) Two days later, the WXYV call sign moved to 105.7 and changed back to an urban contemporary format branding as X105.7, positioning itself against WERQ once again. The call sign swap between the two stations took place 4 days later.[6] In addition, WQSR acquired the rights to Baltimore Ravens games from sister station WLIF, and retained those rights until 2006, when WBAL and WIYY took over. Musically, WQSR's playlist also changed a little, cutting back the pre-1964 songs and some 1980s music was introduced. By 2003, the station was playing strictly songs from 1964 to 1979 with a handful of pre-1964 and post-1979 titles.

On May 4, 2005, at 10:30 a.m., after playing "Na Na Hey Hey Kiss Him Goodbye" by Steam, the station began a half-hour stunt; at 11, the station officially flipped to adult hits, branded as 102-7 Jack FM. The first song on "Jack" was "Hungry Like the Wolf" by Duran Duran.

Infinity Broadcasting would be renamed CBS Radio in December 2005.

On December 15, 2008, CBS Radio announced that it would be swapping WQSR and four of its other medium-market radio stations to Clear Channel Communications for two radio stations, KLOL and KHMX in Houston. Clear Channel took over WQSR at 11:59 p.m. on Tuesday, March 31, 2009. After playing songs at CBS Radio's Baltimore studios such as "End of the Road" by Boyz II Men, R.E.M.'s "It's the End of the World as We Know It (And I Feel Fine)" and "Goodbye Stranger" by Supertramp at roughly 11:57 p.m., the station went to dead air as Clear Channel officially took ownership of the station. Shortly thereafter, the station returned to the air at the Clear Channel Baltimore studios. The sale also resulted in the station reuniting with former sister WCAO under common ownership for the first time since 1998.

WQSR in its current incarnation as Jack FM runs a strictly jockless Variety Hits format. Although there are no on-air personalities on the station, the station airs Casey Kasem's American Top 40: The 1980s on Sunday nights from 7pm-11pm (though before August 4, 2019 the start time was an hour later).