which was attached to a Western Union clock and tripped by the minute hand of the clock, then reset the stepping relay. Originally, 30-minute station identification was accomplished by a simulcast switch in the control booth for sister station WSJM, whereupon the disc jockey in the booth would announce "This is WSJM-AM and... (then pressing the momentary contact button) ...WSJM-FM, St. Joseph, Michigan." 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. A different technology appeared in 1980 with the analog recorders made by Solidyne, which used a computer-controlled tape positioning system. Four GMS 204 units were controlled from a 6809 microprocessor, with the program stored in a solid-state plug-in memory module. This system has a limited programming time of about eight hours. Satellite programming often used audible dual-tone multi-frequency (DTMF) signals to trigger events at affiliate stations. This allowed the automatic local insertion of ads and station IDs. Because there are 12 (or 16) tone pairs, and typically four tones were sent in rapid succession (less than one second), more events could be triggered than by sub-audible tones (usually 25 Hz and 35 Hz). Modern digital systems Modern systems run on hard disk, where all of the music, jingles, advertisements, voice tracks, and other announcements are stored. These audio files may be either compressed or uncompressed, or often with only minimal compression as a compromise between file size and quality. For radio software, these disks are usually in computers, sometimes running their own custom operating systems, but more often running as an application on a PC operating system. Scheduling was an important advance of these systems, allowing for exact timing. Some systems use GPS satellite receivers to obtain exact atomic time, for perfect synchronization with satellite-delivered programming. Reasonably-accurate timekeeping can also be obtained with the use of Internet protocols (IP) like Network Time Protocol (NTP). Automation systems are also more interactive than ever before with digital audio workstation (DAW) with console automation and can even record from a telephone hybrid to play back an edited conversation with a telephone caller. This is part of a system's live-assist mode. The use of automation software and voice tracks to replace live DJs is a current trend in radio broadcasting, done by many Internet radio and adult hits stations. Stations can even be