Here’s an article from ChristianityToday.com about Christian radio. 

Its a four part series about its history and growth, and if it needs fixing.

You can read it here.

This article reminds me of the time I went to lunch with a coworker.  When he started his car the local Christian radio station was on and I asked if he listened to it because he was a believer.  He simply told me he was an atheists but enjoys the positive vibe.