I took three Business Law courses when I was in college, so I can tell you how I would go about it:
First, you go down to the county courthouse or one of the sub-courthouses, and one of the offices will be for "Assumed Name Certificates." They cost about $20. You can either list it for yourself as a Sole Proprietorship, a Partnership, or a Corporation. My advice is to make it as Sole Proprietorship. If you make it a partnership, your partner can obligate you to contracts that you didn't even sign.
With the Assumed Name Certificate, you may now do business with that name, and if you catch a competing radio station trying to use it, you can stop them.
Here's a true story:
You may have heard of Lico Reyes of Parties Portable. That company was originally named Disco Delite, and Lico owned that Assumed Name Certificate.
K104 Radio began having a program of beat-mixed dance music on weekend nights, and the DJ for that show began calling it "The Disco Delight," which sounds the same.
Lico complained to K104 management, but they didn't seem to care.
Then, that DJ began doing mobile DJ parties -- just like Lico was doing -- and he STILL called his business "The Disco Delight" in person AND on the radio.
Lico got an attorney. An injunction was levied, and he received something for damages.
In terms of a "Trademark," you really only need that if you don't want anyone else in the entire United States to use that name. For example, Howard Stern has his name as a Registered Trademark.