GB1488911A - Digital data transmission systems - Google Patents

Abstract

1488911 Digital transmission SIEMENS AG 23 Sept 1974 [21 Sept 1973] 39558/74 Addition to 1473941 Headings H4M and H4P In a digital data transmission system of the type of the parent Specification in which digital data is frequently shifted by 0À5 times the digit frequency before transmission a demodulator and regenerator which is usable either at a repeater or terminal station comprises an input band-pass filter 41 feeding a modulator 42 where the incoming digital signals modulate a carrier of 3À5 times the digit repetition frequency. The lower sideband of the modulated signal is selected by filter 43 and modulated in modulator 44 by a carrier of 3 times the digit repetition frequency to derive base band digital signals which are filtered out by low-pass filter 45. The base band signal is fed through an automatic equalizer 51 to a decision device 53 which provides one output 531 on the positive pulses and a second output 532 on the negative pulses of the bipolar input pulse stream. The respective outputs 531 and 532 are fed to decision devices 57 and 58 where they are retimed by the pulse signal from oscillator 56 whose frequency is locked to the incoming pulse stream frequency by the control loop 54, 55, 56 which is fed with the output from the decision device 53. The oscillator 56 also provides, via a divide by two stage 63 and multipliers 64, 65, the carriers for modulators 42 and 44. The output of the regenerator 50 can be fed to a combining amplifier if the regenerator is at the receiving terminal station, or to the digital double pushpull modulator 61, fed with a carrier derived from oscillator 56 via divider 63, if the regenerator is at a repeater station. The digital modulator 61 can be of the type described in Specification 1,482,971.