Compatible Multichannel FM Broadcast System

The two channel FM Stereo Broadcast System1 in use today was extended by General Electric to a 4-channel system; and, in October 1971 this proposed General Electric 4-channel FM Stereophonic Broadcast System was successfully field-tested on an experimental basis in the Schenectady, New York area over radio station WGFM2. This system is compatible with present two-channel stereophonic and monophonic broadcast receivers, provides equal noise characteristics at the four audio outputs and allows the use of the Subsidiary Communication Authorization (SCA) channel at a higher 95 KHz subcarrier. The system transmits the full audio frequency range of 30 to 15,000 Hz on each of four audio channels and maintains at least 30 db audio separation between each of them. The measured harmonic distortion and intermodulation distortion falls well within the existing FCC requirements for broadcast equipment.