Yup. After over 4 decades in the music and radio business I can reiterate that every point made in the above article is correct.
It doesn't specifically apply to radio broadcasting but is a very good overview. The important thing to note is there is no such thing as a public domain sound recording in the United States. You can of course broadcast public domain songs, provided of course that you or someone you hired to play them is performing them. I still see websites offering public music domain downloads, and there actually aren't any. NO sound recordings AT ALL are public domain. Unless of course you stumble upon a song someone just wrote and recorded and the original author states they just wrote and recorded this and they'v specifically put it in the public domain. There ARE tons of songs with a creative commons license, which depending on the selected terms may be used, but again I warn you, many performers, bands, etc record cover versions of known songs and list them as a creative commons -- in which case their specific performance is public domain, but you still need the rights to the song itself. Although it's possible a musical group might do a recording of a public domain song, then make their performance public domain, or CC, it which cas you found a song to broadcast royalty free. It would take hundreds of hours to find enough PD/CC songs to program a radio station.
There's a quick easy bit on classical recordings here:
http://www.shockwave-sound.com/Articles/010_Copyrights_in_Public_Domain_music.html
If that helps.
Tim in Bovey