Patent GB-1183965-A (GB)
Title: Binary Facsimile Systems and Apparatus
IPC: H04L27/02
Filed: 1967-09-14
Abstract: 1,183,965. Facsimile communication systems; substation equipment. PHONOCOPY Inc. 14 Sept., 1967 [15 Sept., 1966], No. 41915/67. Headings H4F and H4J. Video signals derived by scanning photoelectrically a two-tone document in a unit 11 are amplitude quantized to two levels in a circuit 22, time quantized under the control of 4 kc. clock signals in a circuit 24 to form a modified binary signal, and finally converted to a threelevel signal and modulated on to a carrier in circuits 31, 33, 34, 35 to furnish a signal suitable for transmission over a narrow band-width channel, such as a voice telephone line. Corresponding received signals are detected in'a fullwave envelope detector 56 and applied to a decoder circuit 61 to re-establish a binary signal which may be used for printing a facsimile in unit 11. The translation of the modified binary signal from circuit 24 to a three-level signal is effected by a filter 31 having a 1À4 kc. cut-off frequency. The conversion of the signal back to binary form is effected by full wave envelope detection in detector 56 and the use of logic circuit in decoder 61. The arrangement, is based on U.S. Specification 3,162,724 and make use of the method of " partial response transmission " described in J.F.E.E. Communications Convention, June 1965, pp. 451-455. The signal from filter 31 is amplitude modulated in circuit 34 on a 2À6 kc. carrier signal from oscillator 33 and is applied to the transmission channel through a low-pass filter with a 2À4 kc. cut-off frequency. The signals may be nonnected directly to a telephone line or coupled to the line acoustically through the telephone transmitter. The preferred arrangement, however, (as illustrated) comprises coupling the signals to the telephone receiver magnetically by means of a coil 39. A similar arrangement for receiving signals uses a hum-bucking assembly comprising two coils 51, 52 connected in opposition as regards external magnetic fields. The apparatus illustrated comprises a unitary send/receive equipment which may be established in either mode of operation by actuation of switch 10. The scanner-printer unit 11 is a flat-bed apparatus in which, the document for transmissions or the recording sheet is traversed through the apparatus by rollers 71, 71<SP>1</SP>, driven by motor 14 whilst being- scanned transversely by heads carried on a belt 75 passing over rollers 76 driven by motor 12. Recording is effected by the electro-junction thermograph process described in Specification 1,183,966, in which current passing from a stylus 74 causes local heating of a metal foil or platen 78, whereby a substance is transferred to a paper sheet. During transmission, timing of operations is controlled by a 72 kc. crystal oscillator 28, the output from which is divided to 4 kc. in count-down circuit 27 to furnish the clock signal for circuit 24, and which is further divided by 10 in circuit 13 to furnish the drive for motor 12. During reception, synchronism is established by the received, time-quantized, binary signal which is applied from circuit 61 to the countdown circuit 27. The scanner-printer unit 11 is provided with switches 72-83 which detect respectively the entry and departure of a document or record sheet from the apparatus. Switch 72 directly sets a flip-flop 84 upon closure, whilst switch 85 is connected through an inverter to produce a reset signal when the switch opens. Flip-flop 84 controls motor 14 and a flip-flip-flop 86 which controls motor 12 and an AND gate 93 in the signal output channel. An AND gate 88 is included in the connection from flip-flop 84 so that commencement of operations depends upon a further signal on line 89. For transmission, this is provided by the correct positioning of the send/receive switch 10 to " send "; for reception the signal depends upon the positioning of the switch to " receive " and also the presence of a received carrier signal as indicated by the triggering of a flip-flop 87 in response to a signal on line 91 from detector 56. The reset signal from flip-flop, 84 resets flip-flops 84 and 85. The apparatus includes an equalizer filter 37 whose characteristics are modified for transmission and reception by send/receive switch 10.