| 摘要 |
PURPOSE:To accelerate data transmission without using high level image compression technique by providing a frequency modulator which applies frequency- multiplexed modulation signal to an external modulator, and setting a modulation index so as to provide output spectrum fitted in the amplitude frequency characteristic of the external modulator in the output spectrum of a modulation signal from the frequency modulator. CONSTITUTION:A point different from a conventional system is that an FSK modulator 20 of frequency shift keying FSK system and a demodulator 21 of same system are provided instead of a slow data modulator and a slow data demodulator. The FSK modulator 20 modulates input data to the one of FSK, and outputs an FSK signal with prescribed output spectrum to the external modulator 13. The output spectrum can be widely changed by the modulation index. When two frequency bands f1, f2 used in transmission are prepared, the output spectrum of the FSK signal is divided into two by setting the modulation index at an appropriate value, and most power can be concentrated in the frequency bands f1, f2, which enables fast data transmission equivalent to frequency deviation DELTAf=f1-f2 to be performed. |
