The electromagnetic spectrum is the most heavily regulated form of energy on earth. In the USA Carrier Current stations and Campus Radio stations do not require a license to set up and operate. A carrier current station consists of an AM radio frequency signal on a frequency between 535 and 1705 kHz injected into a power line. They are governed by 47 CFR Sections 15.207(c), 15.209(a), and 15.221 of the Commission’s rules and are accessible in the link provided here.