Patent GB-902655-A (GB)
Title: Call letter keyer
IPC: H04L15/22
Filed: 1959-10-21
Abstract: 902,655. Electric selective signalling systems. ACF. INDUSTRIES Inc. Oct. 21, 1959 [Nov. 26, 1958], No. 35652/59. Class 40 (1). A system for producing electric signals representing call letters comprises in combination switching means settable to select a letter, a commutating device connected to said switching means, a circuit connected to said commutating device to initiate and control the commutation thereof, and a signal source connected to the commutating device to produce a series of output signals each signal having a discrete duration determined by the switching means in such a way that the series of signals represents, in combination, the selected call letter. The system described comprises a plurality of letter generators each manually settable to generate signals representing, in morse code, a selected letter, and so connected in series that each letter generator upon completing the generation of the letter to which it is set initiates operation of the next letter generator. In this way a sequence of letters is generated and each letter is separated from its predecessor by the correct time. In the morse code letters are represented by combinations of dots and dashes: each dot is a unit of time in duration, each dash three units of time, and the space between successive dots or dashes one unit of time. Each letter is separated from the next letter by a space of three units of time. As described, Fig. 3a, each letter generator comprises a commutating multi-cathode tube 123 and a letter selecting switch 110. When operation of a letter generator is initiated a circuit 136 applies pulses to the guide electrodes of the multi-cathode tube causing step-by-step advance of the discharge which results in the potentials on the cathodes (which are normally near earth) rising in succession and the circuit is such that each is positive for one unit of time and a pause of one unit of time elapses before the next cathode goes positive. (During the pause between neighbouring cathodes going positive the discharge is being advanced by the guide electrodes). This would result, but for the action of the letter selecting switch, in a line 114 connected to cathodes 0 to 7 receiving a train of dots (earth) separated by unit spaces (positive), and these signals are used to key a signal generator (not shown) associated with the letter generator. The action of the selecting switch is to bridge the gap between two adjacent dots (earth) to form a dash-three dots in length- and this is effected by preventing line 114 going positive by clamping it to earth. Thus to generate the letter " A " the selector switch is set at "A" and in this position cathode 2 is earth, so that when the discharge advances step-by-step a dot and a dash, see Fig. 1, is produced. When the selector switch is in position " A " cathode 3 is connected to a lead 113 which inhibits generation of any further signals by the signal generator associated with the first letter generator, a cathode 4 is connected to a lead 115 which initiates operation of the next letter generator. This produces the requisite space of three units of time between successive letters.