In Philly, it's WRTI (Temple University's professionally-run NPR affiliate). REAL jazz from 6PM-6AM. (There's also a so-called "smooth jazz" station in Philly that isn't worth mentioning here). WRTI used to have 24-hour jazz, but gave the 6AM-6PM hours over to Classical when the all-classical station here sold out to another format. Frankly, it's ridiculous that Philly, the 4th largest radio market in the country--and home to world-class classical music institutions (Philadelphia Orchestra, Curtis Institute, etc.) and an incredible jazz tradition (Coltrane, Getz, Lee Morgan, Sun Ra, Golson, Philly Joe Jones, and on and on and on . . .) doesn't have either a full-time classical OR a full-time jazz station. Oh well, WRTI says that when they begin broadcasting digital radio, they'll be able to offer both classical and jazz streams during the day.
WRTI has local jazz DJj's, and their star in that regard is Bob Perkins (6-9pm), who sounds like he's been doing it for decades. They also carry the NPR jazz shows.
WRTI.org