Patent GB-844808-A (GB)
Title: Improvements in or relating to facsimile apparatus
Inventor: MASON FREDERICK PERCIVAL
IPC: H04N1/327
Filed: 1958-03-14
Abstract: 844,808. Facsimile apparatus. CREED & CO. Ltd. March 13, 1959 [March 14, 1958], No. 8294/58. Class 40(3). A facsimile transceiver has provision for transmitting an interrupted calling signal to a distant similar transceiver and for receiving, during the interuptions, a go-ahead signal sent back from the distant transceiver. This latter signal is initiated manually on receipt of the calling signal and, when received at the first transceiver, is responded to by the manual initia-  tion of the transmission which consists of a phasing signal of sufficient duration to allow the scanning drums at both stations to reach the same speed (starting from a common datum position) after which transmission of the intelligence on the drum commences. Transmission: To initiate the calling signal a switch is operated from a "stand-by" position, in which all contacts are in the positions shown ("back"), to a "call" position in which it is latched (Fig. 4, not shown). This results in the operation ("up") of contacts CALL 1, 2, 3 (Fig. 2) and CALL 4 (Fig. 1) and the starting-up of a chopper disc motor CH, the scanning drum motor DM and a motor TMA which controls the interruptions in the calling signal and the reception of the go-ahead signal. For this purpose motor TMA is arranged to operate change-over contacts TA/1 between the position shown (back) in which it remains for 2 seconds, and the opposite position (up), in which it remains for 3 seconds and simultaneously, to change over contact TA/2 after intervals of 300 milliseconds. This results in a 1800 c.p.s. tone from G2 being sent to line via TA/1 (up), A/1, and CALL 4 (up) for 3 seconds after which the detector X is conditioned to receive a go-ahead signal consisting of alternate 300 milliseconds "bursts" of a 1800 c.p.s. signal from the called station during the 2 second period of TA/1 (back). When such a signal is received contacts DX/1, DX/2 close and open at this rate (300 m.s.) the former causing a lamp L2 to flash and the latter a buzzer Fl to sound. In response to such indication the calling operator closes a "Send" switch S (Fig. 2) which operates relay A/3 which holds over contact A/3 and starts-up a motor TMB. This results in a phasing signal of frequency 850 c.p.s. being sent to line generator Gl (Fig. 1) via DC1 (back), A/1 (up) and Call 4 (up) and the commencement of a timing operation controlled by motor TMB which concludes in the opening of contact TB/I after 250 milliseconds. The power supply to motor TMA is thus interrupted and the clutch release magnet CRM caused to operate and clutch-in the motor DM to the scanning drum which initially is in a datum position corresponding to the drum at the called station. When the carriage (carrying the optical scanning apparatus) commences to move a switch DC2, controlled by a ratchet type counting arrangement (Fig. 3 not shown), is closed and the scanning light source L3, energized and, at the end of the fifth revolution of the drum, the contacts DC1, also controlled by the arrangement of Fig. 3 (not shown), change over and supply the tone G2 modulated by the information derived from the scanning process to line. At the end of the full scanning cycle the counting arrangement (Fig. 3 not shown) is released thus allowing contacts DC1 and DC2 to revert to normal and the carriage operates contacts CCLH causing a buzzer F2 to sound and operates a relay B/3 which holds over B/1 this latter contact also maintaining power to the buzzer which sounds continuously. Operation of contacts B/2 and B/3 then result in the breaking of the power circuits to the clutch release magnet CRM and to the motor TMB respectively the latter then allowing contact TB/1 to return to the position shown and operation of contacts DCI and DC2 result respectively in the connection of generator G1 to line (the "stop" signal) and the cutting off of the power supply to lamp L3. The apparatus then remains in this condition (the buzzer F2 sounding) until the carriage is manually returned to its initial position which action releases the latched switch (Fig. 4 not shown) from the "call" to the "stand-by" position and allows all contacts still operated to return to the positions shown. Reception: When the apparatus (in the "standby" condition) is employed to receive a transmission from a similar distant apparatus the calling signal consisting of bursts of frequency 1800 c.p.s. of 3 seconds duration separated by 2 second intervals (as described above) is supplied to the detector X (Fig. 1) via Call 4 (back) and Rec. 3 (back) and results in operation of contacts DX/1 and DX/2 (Fig. 2) operating the lamp L1 and the buzzer F1. Action by the operator then consists of adjusting the gain control GC (Fig. 1) to produce a desired signal level as read on M and operation of the switch (Fig. 4 not shown) from "stand-by" to "receive", in which position it is latched. This results in operation of contact Rec. 1 (Fig. 2) which starts-up motors CH, DM and TMA, contact Rec. 2 (Fig. 2) which cuts off H.T. power from detector X and supplies H.T. power to a second detector Y, and contact Rec 3. which connects the line to detector Y via A/2 and TA/2. The rotation of motor TMA operates contacts TA/2 (as described above) and sends bursts of frequency 1800 c.p.s. from G2 to line (the "goahead" signal) during alternate 300 millisecond periods. During the intervening 300 millisecond periods detector Y is connected to line and on receipt of the phasing signal (850 c.p.s. from distant G1 to which Y is responsive) causes contacts DY (Fig. 2) to change over and supply power via Rec. 1 (up), SMS (back) and CC¢ (back) to energize relay A/3 which holds over A/3 and starts-up motor TMB and, at the same time, cuts-off power from motor TMA. Contacts A/1, A/2, and A/3 thus operate (A/1 being ineffective when the apparatus is employed to receive) resulting in the line being connected directly to the gain control GC and detector Y (via Call 4, Rec. 3 and A/2). Contact TB/1 then operate 250 milliseconds after the start of motor TMB (as described above) and when phasing signal ceases and DY returns to normal the clutch release magnet is operated and clutches in the drum to the motor DM. The scanning drum then commences to rotate and the received signal consisting of a modulated 1800 c.p.s. tone (to which detector Y is unresponsive) is supplied directly to the record marking device. In addition to operating contacts DC1, DC2 (which are ineffective during reception) the carriage, when it has moved about ¢ inch, changes over contacts CC ¢ (which are ineffective during transmission) so that, at the termination of the transmission, reception of the "stop" signal (850 c.p.s. from distant Gl) by detector Y operates contact DY again which completes a circuit via DY and CC ¢ to the buzzer F2 and relay B/3 operation of the latter de-energizing the clutch release magnet CRM as described for transmission. If no "stop" is received by the time the carriage has reached the end of its travel contacts CCLH are operated and de-energize CRM, also as described for transmission, buzzer F2 continuing to sound in either case until the carriage is manually reset which action releases the latch held switch (Fig. 4, not shown) from "receive" to "stand-by" position and allows all contacts still operated to return to the positions shown. The mechanical switches TA/1, TA/2 (Fig. 1) may be replaced by electromagnetically coupled change over devices (Fig. 5, not shown) which give improved reliability of operation with the low powers (a few microwatts) sometimes employed in facsimile systems.