Improvements relating to space satellite communications systems

摘要

1,072,019. Space satellite communication systems. G. BATTAIL, and P. BROSSARD. Feb. 28, 1966 [Feb. 27, 1965], No. 8706/66. Heading H4L. The invention is concerned with a communication system, comprising a plurality of land transmitters and receivers utilizing a common space satallite repeater. Each transmitter transmits over the same frequency band and communication is by means of frequency modulation. Allocation of a receiver to a particular transmitter is brought about by adding a distinctive frequency to the communication signal to produce a composite signal and frequency modulating the carrier of the transmitter by said composite signal. The allocated receiver is rendered insensitive to all signals other than that which is frequency modulated by a composite signal comprising said distinctive frequency. At the transmitter station 1, the communication signal at 11 is added in network 12 to a much larger amplitude signal of distinctive frequency F 1 . The produced composite signal, frequency modulates the output of oscillator 15 in modulator 14, to produce a signal which is transmitted to the satellite 2. At the satellite, the carrier frequency is changed and the signal retransmitted to the receiver station 3. At the receiver station, the signal is passed, via a frequency changer 32 to a reception threshold reducing frequency demodulator 33, which has the property of only being sensitive to signals having a low rate of change of frequency. The output of the demodulator 33 is fed to receiver output 34, and also to a filter 35 which selects the frequency F 1 and passes it to a high-gain amplifier 36. The output of the amplifier at frequency F 1 , frequency modulates, in modulator 38, the output of oscillator 37. The resultant frequency modulated signal is passed to the second input of frequency changer (mixer) 32. The result is that the frequency modulation in the received signal due to the added frequency F 1 is cancelled out, and only frequency moduation due to the communication signal appears at the input to demodulator 33 and only the communication signal appears at output 34. The frequencies F 2 . . . F n allocated to other transmitter/receiver station pairs and the corresponding frequency deviations, are so chosen that reception of a signal with an identifying frequency modulation frequency F 2 say produces, at the input to demodulator 33, a beat frequency (F 2 - F 1 ) frequency modulation, with an instantaneous rate of change of frequency so high that the demodulator is insensitive thereto.