There's one radio station group that has consistently been fully public interest with neither ads nor corporate nor government conflicts-of-interest: the Pacifica network which has affiliates around the country http://pacificanetwork.org
"WFMU’s primary source of support comes from listener contributions made during our annual on-air fundraising marathonand revenue generated from our annual Record Fair. WFMU does not accept underwriting or corporate sponsorships. We receive some support from foundations and government grants, as long as they do not contain conditions that determine our programming content or restrict our independence."
I donate every year. It's a great cause to support.
It seems that ads were also a motivation for the long-running show JM in the AM to leave the station.
> WFMU, licensed as a non-profit radio station, adheres to the guidelines of charitable and non-commercial radio. With the move of ‘JM in the AM’ exclusively to NSN, the program, its host, its content and its reach will be allowed greater creative flexibility and sponsorship opportunities.