Broadcast automation

The radio transmitter end of the airchain is handled by a separate automatic transmission system (ATS).

In the U.S., it was also necessary to have an operator on duty at all times in case the Emergency Broadcast System (EBS) was used, as this had to be triggered manually.

While there has not been a requirement to relay any other warnings, any mandatory messages from the U.S. president would have had to first be authenticated with a code word sealed in a pink envelope sent annually to stations by the Federal Communications Commission (FCC).

In the U.S., this came about when the EAS replaced the EBS, starting the movement toward automation to assist, and sometimes take the place of, the live disc jockeys (DJs) and radio personalities.

Advertisements, jingles, and the top-of-hour station identification required by law were commonly stored on Fidelipac endless-loop tape cartridges, known colloquially as "carts".

Because the capstan was already spinning at full speed, tape playback commenced without delay or any audible "run-up".

The tapes played by these machines were originally produced in the Midwest Family Broadcasting (MWF) Madison, Wisconsin production facility by WSJM Chief Engineer Richard E. McLemore (and later in-house at WSJM) with sub-audible tones used to signal the end of a song.

This only lasted about six months, however, and a standard tape cartridge player was wired in to announce the station identification and triggered by the Western Union clock.

Satellite programming often used audible dual-tone multi-frequency (DTMF) signals to trigger events at affiliate stations.

Modern systems run on hard disk, where all of the music, jingles, advertisements, voice tracks, and other announcements are stored.

Some systems use GPS satellite receivers to obtain exact atomic time, for perfect synchronization with satellite-delivered programming.