GB613137A - Improvements in or relating to telegraph transmitters - Google Patents

Abstract

613,137. Type-printing telegraphy; thermionic distributers. STANDARD TELEPHONES & CABLES, Ltd., and DAVIS, L. G. Feb. 18, 1946, No. 5081. [Class 40 (iii)] A telegraph transmitter employing for each signal a sequence of elements of equal duration in which there are only two kinds of element, comprises a chain of electronic devices rendered conducting sequentially by a source of electric oscillations to determine the intervals occupied by the elements of said code and means for determining the kind of element to be transmitted in each interval. The transmitter comprises a closed chain T1 ... T8 of three-electrode coldcathode tubes connected as described in Specification 566,156 and in order to cause it to function a relay STR (not shown) must first be energized. Make-before-break contacts str2 apply positive potential to all the anodes of tubes T 1 ... T8 and whilst bunched also apply positive potential to the control electrode of a stop tube T7 which fires. The consequent anode current energizes the marking winding M of a polarized transmitting relay TR1, whose contacts tr1 send marking current to line L. The voltage drop across cathode resistance R7 is applied to the control electrode of a second stop tube T8, but is insufficient to fire it. A source of alternating potential (conveniently the 50-cycle mains) is applied via a transformer T and closed contacts str1 across a tube T9 which fires on each positive half-cycle and applies a pulse over resistance R25 and condensers C9 ... C16 to the control electrodes of tubes T1 ... T8, causing the partially-energized stop tube T8 to .fire and extinguish tube T7. Succeeding positive half-cycles will fire tubes T1 ... T8 in turn. The anode current which flows in the start tube T1 energizes the spacing winding S of the transmitting relay TR1 and sends a start signal to line. Subsequent energization of each code tube T2 ... T6 in turn will transmit a mark or space according to the position of contacts V ... Z respectively. These may be set, for example, by the operation of a key-board. In this case, the anode lead of tube T1 marked with a cross may be replaced by the dotted circuit in which a contact st is closed upon the depression of any key. The normal condition is then with stop tube T8 fired and marking current sent to line, the transmitter remaining in this condition until a key is depressed. In a modification (Fig. 2, not shown), each of the five contacts V ... Z is replaced by a set of twenty-five make or break contacts in parallel. Each " bank " of five contacts is connected to the spacing and marking windings of the transmitting relay TR1 in such a way that when a " bank " of contacts is closed the sequential firing of the tubes T1 ... T8 transmits a predetermined character. A counting relay-chain is arranged to close the twenty-five " banks " of contacts in turn and transmit such signals as BUSY, DIAL, WHO ARE YOU, and PERF. These signals are transmitted in turn to separate leads and the transmitter may be used at an automatic telegraph exchange in place of a rotary machine transmitter which sends the various signals simultaneously to the separate leads, which are then connected by the exchange apparatus to a subscriber as required. Specification 555,999 also is referred to.