Patent GB-587489-A (GB)
Title: Multiplex telephone system
IPC: H04J3/16
Filed: 1944-09-29
Abstract: 587,489. Multiplex wireless signalling. STANDARD TELEPHONES & CABLES, Ltd. Sept. 29, 1944, No. 18684. Convention date, Oct. 19, 1943. [Class 40 (v)] In a multiplex communication system energy provided by an alternating current source at one of the terminal stations is transmitted over the communication medium to maintain the system in synchronism and is also utilized to energize the equipment at one or more of the stations. Terminal stations 10, 15 are connected by the line 11 which includes repeaters 12, 14, the branch station 13 being connected to the line at an intermediate point. Terminal station 10. Audio signals from the lines 1, 2, 3 pass through corresponding hybrid coils 101 &c., provided with balancing networks 104 &c., to the pulse modulators 107, 108, 109. The combined output is applied via the bandpass filter 113 and high-pass filter 114 to the line 11. Incoming signals at carrier frequency from the line 11 pass through the filter 114 and are separated out by the band-pass filter 133 and applied to the detector 135. The group of rectitied output signals is applied to the channel demodulators 127, 128, 129 which feed the separated signals to their respective lines 1, 2, 3 via the hybrid coils 101 &c. The modulators 107 &c. and demodulators 127 &c. are operated by pulses from the synchronizing source 112 via the phase-shifting networks 117 &c. and 137 &c., respectively. An additional phase-shifter 116 common to the demodulating network compensates for the time-delay on signals from the line 11. The A.C. power source 110 operating at a sub-multiple of the synchronizing frequency, controls the synchronizing source 112, and supplies energy which is rectified at 111. to provide D.C. potentials for the units 107, 127, &c.- The source 110 also supplies A.C. to the line 11 via the low-pass filter 115, which supplies the power to operate the repeaters 12, 14, the A.C. power being transmitted via low-pass filters 22, 23 shunting the repeaters 12, 14, respectively. Terminal station 15. Incoming signals on the line 11 pass via the high-pass filter 314 and band-pass filter 313 to the demodulators 307, 308, 309, the separated signals passing to the corresponding lines over hybrid coils 301 &c. Line signals pass through the hybrid coils 301 &c. to the pulse modulators 327 &c., the combined output from which is applied to the carrier modulator 335. The modulated carrier wave is applied via the band-pass filter 333 and low-pass filter 314 to the line 11. A.C. power from the station 10 is separated off the line 11. by the low-pass filter 315 and applied to a synchronizer 334 controlling a local source of power 310 and the synchronizing source 312. The source 312 supplies operating pulses to the demodulators 307 &c., and modulators 327 &c., via phase-shifters 317 &c., 337 &c., respectively, an additional phase-shifter 336 in the modulating network taking care of the transmission time of the line. Branch terminal 13. Signals on the line 11 from the station 10 pass through the high-pass filter 214 and band-pass filter 213 to the pulso demodulator 207. The audio output signal passes through a high-pass filter 241 and the hybrid coil 242 to the line 246. Ringing tones when present in the audio signal pass via filter 240 to operate a relay 244, the intermittent closing of the contacts 245 causing a ringing tone to be produced on the line 246. Signals from the line 246 for the station 10 pass via the hybrid coil 242 to the pulse modulator 227 and thence to the carrier modulator 235 which applies them via the band-pass filter 233 and filter 214 to the line 11. A.C. power from the station 10 is separated off the line 11 by the low-pass filter 215 and applied to a rectifier 211 to supply D.C. power for the station 13. It is also applied to control the synchronizing oscillator 212 which supplies operating pulses to the demodulator 207 and modulator 227 through the phase-shifting networks 217, 237, respectively. Signals on the line 11 from the station 15 pass through the filter 214 and band-pass filter 233 to the carrier detector 257, pulse demodulator 228 and hence via. the hybrid coil 252 to the line 256. Filters 250, 251 and the relay 254 apply ringing tones to the line 256. Signals from the line 256 for the station 15 are applied to the pulse modulator 208 and hence via the filters 213, 214 to the line 11. The modulator 208 and demodulator 228 derive pulses from the oscillator 212 via phaseshifters 218, 238, respectively. The pairs of phase-shifters 217, 237 and 218, 238 respectively may be made adjustable in order to select the channels on which communication with the stations 10, 15 respectively is set up. Specification 509,820is referred to.