Waht falls under copyright in the US is described in
17 USC §102, and the whole question hinges on the bolded part:
(a)Copyright protection subsists, in accordance with this title, in original works of authorship fixed in any tangible medium of expression, [...]
The radio transmission itself thus does not fall under copyright, as it is not fixed in a tangible medium while it travels through the air, and it is not a sound recording under 17 USC 102 (a)7 either.
As such, normal discussions on the bands like Alice talking to Bob, does not even create a copyright in the first place. That is not regulated in FCC rules, it falls directly from the copyright law: because the material is not fixed, it is not copyrighted in the first place. That is, if nobody fixed or fixes the transmission, nobody owns them. That doesn't mean the contents are public domain:
However the contents of the transmission can be under copyright anyway and transmitting them might be copyright infringement (aka "Radio Piracy" or "Pirate Radio"): you could play a recording of a song via amateur radio, which is under copyright, or you could read a book which is under copyright, and that would violate the author's copyrights if you don't have license to do so. But even if you have a license, transmitting does not put the materials into the public domain: it is a fixed expression (replayed on amateur band) and thus copyrighted.
Nothing in copyright law would turn a transmitted copyrighted material into the public domain - that requires an express release into it.
But it's complicated...
Now, it gets really complicated if we introduce simultaneously fixing the material. Now, the same rules apply as they do when you record a visiting speaker. Or rather, the same setup as a studio and the musicians using it.
Alice creates copyrighted material at home
If Alice loops her signal through a recording box somewhere on her side, the material gets fixed while she is sending. That means it is copyrighted material, and Alice has the copyrights in the original recording, as she both creates the material and records it.
Alice also might own the copyright in the script or notes she used, but that's beside the point.
Bob creates copyrighted material from afar
Let's assume Alice never thought about recording and just airs her material into the night without infringing on other people's copyrights.
But now let's assume Bob, 3 counties over, is also recording Alice signal, and thus fixing the material. Bob had no creative input besides the recording, but the material is now fixed. Bob had some technical and arguably creative input into that recording by choosing the filter settings on his radio setup, antenna placement, and such.
Bob for sure does own a copyright in the recording itself, especially in the alterations he made. However, he would not gain copyright over the material that Alice introduced, which now became fixed by Bob's action. In a strange fashion, Bob turned Alice's speech into a copyrighted tangible expression, and the recording is in a very strange place:
- Bob owns the "Master" itself, and the technical changes that he did.
- Alice owns the contents of the recording, as in her voice input and choice of words.
Distribution of this recording would require both Bob's and Alice's consent now, or Fair Use.
Alice clawing back the rights!
But Alice can circumvent Bob's copyright at any time by simply re-recording her show, and Bob can not claim copyright on that different recording - that was exactly what Taylor Swift did in 2019.
