Patent GB-677757-A (GB)
Title: Electronic telegraph relay circuits
Inventor: TERRY VICTOR JOHN
IPC: H04L25/24
Filed: 1950-10-06
Abstract: 677,757. Telegraphy. STANDARD TELEPHONES & CABLES, Ltd. Oct. 6, 1950, No. 24450/50. Class 40 (iii). An electronic relay circuit for transmitting telegraph signals to a line having distributed impedance employs a transformer to produce transient induced currents at each change in the signal for application to the line as extra charging and discharging currents to correct for the distortion introduced by the distributed impedance. In a single-current circuit, Fig. 1, a tetrode 4 is connected as a cathode follower to transmit signals from transmitting device 5 to line 6 feeding a receiving device 7. The tetrode is cut off on space signals and is rendered conducting to pass current into the line on mark signals. As the current in the valve increases (curve 15, Fig. 2), the current change in transformer 2 induces secondary potentials causing the lower ends of windings 8 and 9 to go positive, whereby current (curve 16, Fig. 2) flows through rectifier 11 to supplement the line current at the commencement of the signal. When device 5 reverts to spacing the tetrode current falls to zero and the induced potentials in windings 8 and 9 reverse. Rectfier 10 conducts and a reverse' current (curve 16, Fig. 2) is drained from the line. In Fig. 2, curve 14 shows the resulting modified current fed to the line, and curve 13 the voltage. A modification (Fig. 3, not shown), includes an amplifying valve connected across the input to the line and arranged to increase the amount of feed-back to the cathode follower to reduce the diasymmetry in cathode-impedance between current and no-current conditions. A single secondary winding is employed in place of windings 8 and 9 shown in Fig. 1. A tapped winding may be employed if it is necessary for the ratios to differ. A further modification, Fig. 4 (not shown), employs a circuit in which the line is connected in the anode circuit of the tetrode. Additional feed-back via a further valve is provided, and rectifiers 10 and 11 are replaced by gas discharge tubes. In Fig. 5 a circuit is shown for double-current working. Tetrode 29 provides the marking current, its cathode being connected to a negative potential and its anode extending to earth through line 37. Tetrode 31 provides the spacing current, its anode being connected to a positive potential and its cathode circuit extending to earth through the line. On mark signals transmitting device 26 applies positive potential to valves 29 and 30 causing them to conduct. Valve 29 passes mark current to line and valve 30 cuts off space valve 31 over anode resistor 35. On space signals valves 29 and 30 are cut off and valve 31 conducts to pass space current to line. The anodes of valves 29 and 31 are connected through separate primary windings 34 and 32 of a transformer, and at each transition between mark and space conditions an induced current is sent from the secondary winding 39 through gas discharge tube 40 to supplement the line current. Tube 40 is a reversible tube comprising main electrodes 41, 42, a trigger electrode 43 returned to a positive potential, and a trigger electrode 44. returned to a negative potential. When space tube 31 becomes conducting the induced potential in winding 39 reduces the potential on electrode 41, causing the gap 41 to 43 to discharge. The discharge then spreads to the main gap 41 to 42, the latter electrode functioning as an anode. When the mark tube 29 conducts, the induced potential is reversed, sending electrode 41 positive and causing gap 41 to 44 to discharge. The discharge again spreads to the main gap, in this case, however, electrode 41 is the anode so that the current fed into the line is reversed. Non-linear resistances may be employed in place of the rectifiers or gas discharge tubes.