Patent GB-284189-A (GB)
Title: Improvements in or relating to telegraph systems and circuit arrangements therefor
IPC: H04L25/26
Filed: 1926-09-21
Abstract: 284,189. Smith, W. S., McLachlan, N. W., and Jacob, W. G. R. Sept. 21, 1926. Systems employing non-contact-making relays; systems using code elements distinguished by polarity of current.-A telegraphic relay system described in connection with a transmitter in which light-sensitive cells are controlled by automatic tape, but applicable also for recording, regenerating or automatic perforating, comprises an arrangement of spark-gaps which are selectively broken down so as to control the polarity of the output current. Thus in the arrangement shown in Fig. 3 the grid potentials of the valves 26, 27 are controlled by light-sensitive cells (not shown) which are themselves controlled by a tape transmitter. The valves are normally rendered non-conductive by a negative grid bias, but when the valve 26, for instance, is rendered conductive through illumination of the corresponding photoelectric cell (not shown), current from the alternator 29 energizes the spark gap 74' and so connects the terminal 100 to the positive end of the battery 49<1>, the middle point of which is connected to the terminal 101. Similarly, when the valve 27 is opened, the terminal 100 is connected to the negative end of the battery through the spark gap 75'. In a modification (Fig. 4, not shown) the spark gaps 74', 75<1> respectively close the circuits of a dot selector mechanism and a. dash selector mechanism. In the arrangement shown in Fig. 2 the control currents from cells 11, 12 are applied after amplification to a pair of valves 26, 27, whose plate circuits include an alternator 29, condenser 68 and coils 30, 31, 32, 33 shunted by a battery 65 and choking circuits 66, 67. Current from the alternator passes through transformer primaries 36, 37 and, in the absence of signals, the spark gaps 69, 70, 71, 72 are broken down by the voltage in the secondaries 42, 43, so that the cable 54 is connected to earth 54' through the spark gaps. When, however, the upper cell 11 acts to render the valves 27 conductive, alternating current from the generator 29 flows in the plate circuit of this valve and, the primaries 31, 37 being wound in opposition to one another, inhibits the sparking at the gaps 69, 70. At the same time the spark gaps 73, 74 are broken down through the transformer 33, 41, so that the cable 54 is now disconnected from the positive end of the battery 49 and connected to its negative end. A negative current therefore flows from earth through the gap 72, battery 49, and gap 73. If, on the other hand, the lower cell 12 be activated, the valve 26 acts similarly to close the spark gaps 71, 72 and open the gaps 75, 76, so that a positive current may flow from earth to cable. Choking circuits are provided as shown to confine the a.c. to the desired channels. In a modification the battery 65 may be dispensed with and the impedances 38, 39 replaced by rectifying valves. In another modification (Fig. 1, not shown) only two spark gaps are employed, each having, however, a central third electrode which divides the gap into two halves. In the absence of signals, one half of each gap is energized, and the cable is earthed through the two remaining half-gaps. The occurrence of a signal de-energizes one halfgap and energizes another, the connections being such that a battery is thereby brought into circuit between cable and earth. The apparatus described can be used for the reception or retransmission as well as for the transmission of signals, incoming signals being applied to the valves 18, 19, while a recorder or retransmitter takes the place of the cable 54.