A radio station is a site configured for broadcasting sound. Traditionally, radio stations have broadcast through the air via radio waves (a form of electromagnetic radiation), sent through a transmitter and antenna. Today, many if not most stations broadcast via cable FM, local wire networks, satellite, or the Internet as well as (or instead of) atmospheric broadcasting. Often stations are linked in radio networks, either in syndication or simulcast, or both.
Radio stations are of a number of types. The best known are the AM and FM stations, both commercial and public or nonprofit. Many college radio or university radio stations are found throughout the developed world.
The earliest radio stations were simply radio telegraph systems, and didn't carry audio. The first known audio transmission that could be called a broadcast occurred on Christmas Eve in 1906, and was made by Reginald Fessenden. While many early experimenters attempted to create systems similar to radiotelephone devices where only two parties were meant to communicate, there were others who intended to transmit to larger audiences. Charles Herrold started broadcasting in California in 1909 and was carrying audio by the next year.
For the next decade, radio tinkerers had to build their own radio receivers. KDKA AM of Pittsburgh, Pennsylvania (owned by Westinghouse) started broadcasting as the first "commercial" radio station on November 2, 1920. The commercial sense of the station came from the type of license—they didn't start airing advertisements until a few years later. The first broadcast was the results of the U.S. presidential election, 1920. Many historians base KDKA's status as "first" on the fact that commercially-produced radio receivers weren't available until that time. However, by that standard, many believe that other stations should count, as at least one smaller manufacturer with their own station was making radios by the time KDKA was licensed.
AM stations occurred first. AM refers to amplitude modulation, a mode of broadcasting radio waves, and occurs on North American airwaves in the mediumwave frequency range of 530 to 1700kHz (known as the "standard broadcast band"). The nine channels from 1620 to 1700 were added as part of the expanded band in the 1990s. Channels are spaced every 10kHz in the Americas, and generally every 9kHz everywhere else. Europe also uses the longwave band.
FM refers to frequency modulation, and occurs on VHF airwaves everywhere (except Japan) in the frequency range of 88 to 108 MHz. Japan uses the 74 to 90MHz band. FM stations are nowadays much more popular in the developed countries, such as Europe and United States today, especially since higher musical fidelity and better stereo broadcasting is possible in this format.
The emerging digital radio stations have started their transmissions, first in Europe (the U.K. and Germany), and later in the United States. The European system is named DAB, for Digital Audio Broadcasting, and uses the public domain EUREKA 147 system. In the United States, the IBOC system is named HD Radio and owned by a private company, a consortium called iBiquity. It is expected that for the next 10 to 20 years, all these systems will co-exist, while from 2015 to 2020, the main system, at least in the developed countries, will be the digital radio.
Many other non-broadcast types of radio stations exist. These include: