Inter-Unit Digital Signal Transmitting Method, Digital Signal Transmitter and Receiver Equipment, Digital Signal Transmitter, and Digital Signal Receiver

1. A digital signal transmitting method for transmitting digital signals to outside of a digital signal transmitter separately including a first transmitter and a second transmitter connected to the first transmitter via a transfer line to which a dc power source is connected, said method comprising the steps of: (a) frequency shift keying (FSK) modulating the digital signals to a lower frequency than an intermediate frequency in the first transmitter to enable the transfer of said digital signals of said lower frequency from the first transmitter to the second transmitter through the transfer line; (b) FSK demodulating the FSK-modulated digital signals of said lower frequency in the second transmitter upon transfer of the digital signals from the first transmitter to the second transmitter via the transfer line; (c) modulating the FSK-demodulated digital signals of said lower frequency into those of said intermediate frequency in the second transmitter; and (d) converting said intermediate frequency of the digital signals to a higher frequency in the second transmitter for transmitting the digital signals to outside ofthe digital signal transmitter.

2. A digital signal receiving method for receiving digital signals from outside of a digital signal receiver separately including a first receiver and a second receiver connected to the first receiver via a transfer line to which a dc power source is connected, said method comprising the steps of: (a) converting a frequency of digital signals received by the first receiver from the outside the digital signal receiver into an intermediate frequency from a higher frequency; (b) demodulating said intermediate frequency of the digital signals to a lower frequency in the first receiver; (c) frequency shift keying (FSK) modulating the digital signals of said lower frequency in the first receiver to enable the transfer of said digital signals of said lower frequency from the first receiver to the second receiver through the transfer line; and (d) FSK demodulating the FSK-modulated digital signals of said lower frequency in the second receiver upon transfer of the digital signals from the first receiver to the second receiver via the transfer line.

3. A digital signal transmitter/receiver system in a multi-equipment form for transmitting and receiving between one digital signal transmitter/receiver equipment and another identical digital signal transmitter/receiver equipment, each digital signal transmitter/receiver equipment separately comprising: a first transmitter/receiver unit and a second transmitter/receiver unit connected to said first transmitter/receiver unit via a transfer line, to which a dc power source is connected; a first frequency shift keying (FSK) modulation unit in said first transmitter/receiver unit for FSK modulating digital signals to a lower transmitting frequency than an intermediate transmitting frequency for transferring the digital signals from said first transmitter/receiver unit to said second transmitter/receiver unit via said transfer line; a first FSK demodulation unit in said second transmitter/receiver unit for FSK demodulating the digital signals of said lower transmitting frequency, which are transferred from said first transmitter/receiver unit to said second transmitter/receiver unit via said transmission line; a modulation unit disposed in said second transmitter/receiver unit for modulating said lower transmitting frequency of the FSK-demodulated digital signals output from said FSK demodulation unit to said intermediate transmitting frequency; a first converter in said second transmitter/receiver unit for converting said intermediate transmitting frequency of the digital signals into a higher transmitting frequency for transmitting the digital signals from said one transmitter/receiver equipment; a second converter in said second transmitter/receiver unit for converting a receiving frequency of the digital signals, which are received from outside of said one transmitter/receiver equipment, from a higher receiving frequency to an intermediate receiving frequency lower than said higher receiving frequency; a demodulation unit disposed in said second transmitter/receiver unit for demodulating said intermediate receiving frequency of the digital signals output from said second converter into a lower receiving frequency; a second FSK modulation unit in said second transmitter/receiver unit for FSK modulating the digital signals of said lower receiving frequency output from said demodulation unit for transferring the digital signals from said second transmitter/receiver unit to said first transmitter/receiver unit via said transfer line; and a second FSK demodulation unit in said first transmitter/receiver unit for FSK demodulating the digital signals of said lower receiving frequency.

4. Digital signal transmitter/receiver equipment separately including a first transmitter/receiver unit and a second transmitter/receiver unit connected to said first transmitter/receiver unit via a transfer line to which a dc power source is connected, said equipment comprising: a first frequency shift keying (FSK) modulation unit, in said first transmitter/receiver unit for FSK modulating digital signals to a lower transmitting frequency than an intermediate transmitting frequency for transferring the digital signals from said first transmitter/receiver unit to said second transmitter/receiver unit via said transfer line; a first FSK demodulation unit in said second transmitter/receiver unit for FSK demodulating the digital signals of said lower transmitting frequency, which are transferred from said first transmitter/receiver unit to said second transmitter/receiver unit via said transfer line; a modulation unit disposed in said second transmitter/receiver unit for modulating said lower transmitting frequency of the FSK-demodulated digital signals output from said FSK demodulation unit to said intermediate transmitting frequency; a first converter in said second transmitter/receiver unit for converting said intermediate transmitting frequency of the digital signals into a higher transmitting frequency for transmission of the digital signals from said transmitter/receiver equipment; a second convertor in said second transmitter/receiver unit for converting a receiving frequency of digital signals which are received from outside of said transmitter/receiver equipment, from a higher receiving frequency to an intermediate receiving frequency lower than said higher receiving frequency; a demodulation unit disposed in said second transmitter/receiver unit for demodulating said intermediate receiving frequency of the digital signals output from second converter into a lower receiving frequency; a second FSK modulation unit in said second transmitter/receiver unit for FSK modulating the digital signals of said lower receiving frequency output from said demodulation unit for transferring the digital signals from said second transmitter/receiver unit to said first transmitter/receiver unit via said transfer line; and a second FSK demodulation unit in said first transmitter/receiver unit for FSK demodulating the digital signals of said lower receiving frequency.

5. A digital signal transmitter separately including a first transmitter and a second transmitter connected to said first transmitter via a transfer line, to which a dc power source is connected, comprising: a frequency shift keying (FSK) modulation unit disposed in said first transmitter for FSK modulating digital signals to a lower frequency than an intermediate frequency to enable the transfer of said digital signals from said first transmitter to said second transmitter through the transfer line; an FSK demodulation unit disposed in said second transmitter for FSK demodulating said FSK-modulated digital signals of said lower frequency transferred via the transfer line; a modulation unit disposed in said second transmitter for modulating said FSK-demodulated digital signals of said lower frequency output from said FSK demodulation unit to said intermediate frequency; and a converter unit disposed in said second transmitter for converting said intermediate frequency of said digital signals to a higher frequency than said intermediate frequency.

6. A digital signal receiver separately including a first receiver and a second receiver connected to said first receiver via a transfer line, to which a dc power source is connected, comprising: a converter unit disposed in said first receiver for converting a frequency of digital signals, which are received from outside said digital signal receiver, into an intermediate frequency from a higher frequency than said intermediate frequency; a demodulation unit disposed in said first receiver for demodulating said intermediate frequency of said digital signals to a lower frequency; a frequency shift keying (FSK) modulation unit disposed in said first receiver for FSK modulating said digital signals of said lower frequency to enable the transfer of said digital signals from said first receiver to said second receiver through the transfer line; and an FSK demodulation unit disposed in said second receiver for FSK demodulating said FSK-modulated digital signals of said lower frequency transferred via the transfer line.

7. A digital signal transmitter/receiver system comprising: a digital signal transmitter separately including a first transmitter and a second transmitter connected to said first transmitter via a first transfer line, to which a first dc power source is connected, for transferring digital signals from said first transmitter to said second transmitter; said digital signal transmitter further including a first frequency shift keying (FSK) modulation unit disposed in said first transmitter for FSK modulating said digital signals to a lower transmitting frequency than an intermediate transmitting frequency for transferring the digital signals from said first transmitter to said second transmitter; a first FSK demodulation unit disposed in said second transmitter for FSK demodulating said FSK-modulated digital signals of said lower transmitting frequency; a modulation unit disposed in said second transmitter for modulating said lower transmitting frequency of said digital signals output from said first FSK demodulation unit to said intermediate transmitting frequency; a first converter unit disposed in said second transmitter for converting said intermediate transmitting frequency of said digital signals into a higher frequency than said intermediate transmitting frequency; a digital signal receiver separately including a first receiver for receiving said digital signals of said higher frequency, which are transmitted from said second transmitter, and a second receiver connected to said first receiver via a second receiver connected to said first receiver via a second transfer line, to which a second dc power source is connected for transferring said the digital signals from said first receiver to said second receiver; said digital signal receiver further including a second converter disposed in said first receiver for converting said higher frequency of the received digital signals into an intermediate receiving frequency lower than said higher frequency; a demodulation unit disposed in said first receiver for demodulating said intermediate receiving frequency of said digital signals output from said second converter to a lower receiving frequency than said intermediate receiving frequency; a second FSK modulation unit disposed in said first receiver for FSK modulating said digital signals of said lower receiving frequency for transferring said digital signals from said first receiver to said second receiver; and a second FSK demodulation unit disposed in said second receiver for FSK demodulating said FSK-modulated digital signals of said lower receiver frequency.

8. The digital signal transmitter/receiver equipment according to claim 4, wherein said transmission line between said first and second transmitter/receiver units comprises a transmission line shared for transmission and reception.

9. The digital signal transmitter/receiver equipment according to claim 4, wherein said transmission line between said first and second transmitter/receiver units comprises separately a sending transmission line and a receiving transmission line.

10. The digital signal transmitter according to claim 5, wherein said first transmitter includes bipolar/unipolar converting means and CMI encoding means that are connected to the front stage of said frequency-shift modulation unit, said bipolarlunipolar converting means converting a bipolar signal into a unipolar signal, said CMI coding means subjecting the unipolar signal converted by said bipolar/unipolar converting means to a CMI encoding process; and wherein said second transmitter includes CMI decoding means connected to the rear stage of said frequency-shift demodulation unit, for decoding the signal encoded by said CMI encoding means.

11. The digital signal receiver according to claim 6, wherein said first receiver includes CMI encoding means connected to the front stage of said frequency-shift modulation unit, for subjecting the demodulated unipolar signal to a CMI encoding process; and wherein said second receiver includes CMI decoding means and bipolar/unipolar converting means each connected to the rear stage of said frequency-shift demodulation unit, said CMI decoding means decoding the unipolar signal encoded by said CMI encoding means; and said unipolar/bipolar converting means converting a unipolar signal decoded by said CMI decoding means into a bipolar signal.

12. The digital signal transmitter/receiver system according to claim 7, wherein said first and second transmission lines are a single transmission line.