Unlicensed Broadcasting
Part 15 / subpart C of the rules of the Federal Communications Commission govern the use of “Intentional Radiators.” These are the regulations that apply to users who want to broadcast without a license on the AM band. These regulations outline the technical details regarding field strength, power, and transmitter frequency accuracy and permitted spurious emission limits. The original and full texts of these various sections are below. However, the most pertinent regulations for most Part 15 broadcasters include:
15.209 - Radiated emission limits; general requirements
15.219 - Operation in the band 510-1705 kHz.
15.221 - Operation in the band 525-1705 kHz.
15.239 - Operation in the band 88-108 MHz. (for FM)

All part 15 sections are conveniently available at this FCC web site. There are also some pretty good resources provided by the FCC including this web site tilted “Low Power Broadcast Radio Stations and this federally authored document entitled “Understanding the FCC Regulations for Low-Power, Non-Licensed Transmitters

Unlicensed Broadcasting for Educational Institutions
Special provisions were enacted by the FCC in 1990 which allow the relatively unrestricted broadcasting of an AM signal that remains contained with on the campus or grounds of this institution. As long as the signal is contained to the owned property of this institution, no content, antenna, or output power restrictions are enforced.
Specific regulations are highlighted on this rulemaking notice. Available products from Radio Systems can be found at their Low Power AM Radio and their free radiate page.

Licensed Low-Power Broadcasting for Government Entities and Municipalities
Under PART 9O.242, within the “Private land Mobile Radio Services” section of the FCC rules are regulations for the use of “Travelers Information Radio Stations,” available only for use by Government entities (State Parks, Highway authorities, municipalities, etc.) More information is available at this FCC web site the rulemaking is per this document and from our distributor, Information Station Specialists.
To avoid competition and confusion with licensed commercial stations that share the AM band, TIS stations are restricted from airing commercials, music and must band limit their frequency response above 3000 cycles.