GB1216826A - Unsynchronized partial response binary signalling - Google Patents

Abstract

1,216,826. Facsimile digital communication systems. PHONOCOPY Inc. 3 April, 1969 [5 April, 1968], No. 17573/69. Headings H4F and H4P. In a facsimile transmission system signals from a photo-electric scanner 11 are converted at 13 to binary form, the binary signal a, Fig. 6, passing to a filter 15 having a characteristic defined in the Specification. The resulting partial response signal passes via balanced modulator 16 and v.s.b. filter 24 to a coil associated with a telephone hand-set transmitter 27. Signals received by the handset receiver pass via a.g.c. amplifier 31, equalizer 32, to detector 33 which outputs a signal d, Fig. 6, to threshold unit 35 having the decision level shown and developing a binary signal e which is identical to that (a) at the transmitter and is fed to the facsimile printer. When a document is placed in transmitter scanner 11, monostable 42 is triggered causing unit 53 to issue a signal corresponding to grey level (i.e. mid-way between black and white) for transmission prior to the facsimile signals. At the receiver, when detector 33 receives a carrier signal, unit 38 is enabled and starts the printer 11 in synchronism with the scanner at the transmitter. Unit 38 also triggers monostable 38 which enables gate 43 to pass clock pulses to counter 45 which counts forward or backwards dependent on the level of the output from threshold unit 45. The counter controls the a.g.c. level of amplifier 31.