of those frequencies, to facilitate enforcement of the rules, and to facilitate the participation by anyone who obtains the proper knowledge and equipment, it is illegal to transmit in a way that "obscures the meaning" of the transmission to people who would want to listen in. So, for example, morse code and ASCII are the only exceptable digital codes, and various modulation techniques are standardized as the technologies are developed.
That kind of explains why encryption is not allowed on ham bands, but it doesn't satisfy me. The difference between ham and other bands, is to use other frequencies I've got to pay the FCC major money for a license, or pay some commercial service provider who payed the FCC major money. With ham, I don't have to pay no one nothing, except maybe $10 for a ham license. ham, or some other frequency reserved to work like ham, could easily serve as a poor man's connection to the internet. Anyone with a desktop PC can invest another hundred dollars or so, and have a really low bandwith (2400bps) direct connection to the internet. You can do IP over ham, although it's really dificult to do so currently without breaking the law and losing your license. A public ham or ham-like radio band would seem to be something the cypherpunks would really like. It would definitely facillitate the creation of a sort of blacknet type thing. The government has given the public citizens band, and ham radio, if they're not going to open up ham so it can be used in the ways I'm thinking of, why not take another hunk of spectrum and give it to the public, specifically intended for digital transmissions (IP or otherwise). This seems to be something we should be campaigning for, and the EFF should be lobbying for. Of course, the reason "why not" is because the government can make tons of money by selling the spectrum to Microsoft instead.