GB1398152A - Circuitry for redicing the bandwidth of an information signal - Google Patents

Abstract

1398152 Bandwidth compression system; facsimile system FUJI XEROX CO Ltd 28 July 1972 [29 July 1971] 35529/72 Headings H4R and H4F The bandwidth of a facsimile signal is reduced for transmission by detecting successive intervals of the signal where each interval corresponds to the time between successive predetermined crossings of a reference level, very close to zero level, and inverting alternal signal intervals and passing the signals through a low pass filter. As described negative going crossings of a level close to zero level of the unidirectional facsimile signal Fig. 2a (not shown), causes generation of pulses in circuit 4, Fig. 1, to trigger a bi-stable circuit 5 from one state to the opposite state and produce gating signals e3 and e4 which gate alternate segments of the input signal between negative going zero crossings through gates 6 and 7. The output of gate 6 feeds direct to the adder 9 while the output of gate 7 is inverted before feeding to adder 9. The resulting signal, with alternate segments inverted, is fed to the transmission circuit 11 via a low pass filter 10. At the receiver, Fig. 3, positive going portions of the signal feed through a channel including amplifier 15 while negative going portions of the signal including amplifier 16 and inverter 17 to an adder 18 where the normal and inverted portions are added to restore, after low pass filter 19, the original signal.