Editing AM broadcasting (section)

===Other distribution methods===
{{Main|Carrier current}}
Beginning in the mid-1930s, starting with "[[WBRU#Beginnings|The Brown Network]]" at Brown University in Providence, Rhode Island, a very low power broadcasting method known as [[carrier current]] was developed, and mostly adopted on U.S. college campuses. In this approach AM broadcast signals are distributed over electric power lines, which radiate a signal receivable at a short distance from the lines.<ref>''The Gas Pipe Networks'' by Louis M. Bloch, Jr, 1980.</ref> In Switzerland a system known as "wire broadcasting" (''Telefonrundspruch'' in German) transmitted AM signals over telephone lines in the [[longwave]] band until 1998, when it was shut down.<ref>{{cite web|url=http://www.biennophone.ch/telefonrundspruch.htm|title=Sammlung alter Biennophone-Radios|publisher=Biennophone.ch|access-date=23 July 2017}}</ref> In the UK, [[Rediffusion]] was an early pioneer of AM radio cable distribution.

Hybrid digital broadcast systems, which combine (mono analog) AM transmission with digital sidebands, have started to be used around the world. In the United States, [[iBiquity]]'s proprietary [[HD Radio]] has been adopted and approved by the FCC for medium wave transmissions,<ref>[https://www.fcc.gov/media/radio/digital-radio "Digital Radio"] (fcc.gov)</ref> while [[Digital Radio Mondiale]] is a more open effort often used on the [[shortwave bands]], and can be used alongside many AM broadcasts. Both of these standards are capable of broadcasting audio of significantly greater fidelity than that of standard AM with current bandwidth limitations, and a theoretical frequency response of 0–16&nbsp;kHz, in addition to stereo sound and text data.