| 摘要 |
In a teaching system having a central or master station and one or more student stations remote from the master station, there are provided, at the master station, at least one source of main signals in a first frequency band, which source may be constituted by a tape or other record player for reproducing teaching or instructional materials, a microphone or other source of audio signals from a proctor or supervisor of the teaching system, and a source of control signals which may include address signals for identifying one of the student stations and command signals for controlling various operations of the addressed student station. The audio and control signals are employed to modulate respective carriers so as to provide first and second auxiliary signals, respectively, in frequency bands which are removed from each other and from the first frequency band of the main signals, whereupon the main signals and the first and second auxiliary signals are multiplexed to provide a composite signal which, in turn, modulates a carrier of predetermined frequency suitable for being transmitted to each of the student stations.
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