| 摘要 |
PURPOSE:To attain the fully duplex communication of a drawing signal by eliminating a part of a sound signal band, moving a part of band to form a compressed sound signal having a no-signal band in the voice band to transmitt/ receive the signal and inserting a MODEM signal of plural channels into the no-signal band to transmitt/receive the signal. CONSTITUTION:The frequency range of 0.3-3.4kHz in the sound signal band in an analog telephone line is split into five bands of (1)-(5). The bands at the interval of one band, (1), (3) and (5) are extracted, the position and direction of the band (3) are changed to generate the sound signal of the frequency arrangement as shown in figure 2. A 2-channel drawing signal having the spectrum of a 300bps is generated as shown in 3 in figure at the location at the middle of the bands (1), (3) in figure 2. The sound signal and the drawn picture signal are superimposed in this way to generate a transmission signal shown in 4 in figure. Thus, the sound signal is subjected to full duplex and the drawing signal is also subjected to full duplex by using each one channel for the 2- channel drawing signal for forward/return path.
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