Patent GB-315791-A (GB)
Title: Improvements in telegraph repeating devices
IPC: H04L25/24
Filed: 1929-07-12
Abstract: 315,791. Electrical Research Products, Inc., (Assignees of Burton, E. T.). July 18, 1928, [Convention date]. Restoring imperfect signals.-Strong positive, negative and zero signals are repeated at a predetermined output strength which is independent of the input strength, but signals weaker than a certain marginal strength are not repeated. The system can be used for squaring the wave-form of distorted signals and for suppressing isolated impulses of unit length. In the arrangement shown in Fig. 1 the resistance 5 is equal to the normal output resistance of the valve RT. The output voltage e, of this valve is therefore normally zero, the voltage drop in the resistance 5 neutralizing the voltage of the battery 6. A negative input signal whose strength exceeds a definite value inhibits the anode current of the valve RT, so that the full voltage of the battery 6 is applied to the grid of the valve 'TT, while a sufficiently strong positive signal reduces the filament-anode resistance of the valve RT to a value negligible in comparison with the resistance 5. The current in resistance 5 is therefore doubled, and the voltage drop in it is double the voltage of the battery 6, but opposite in sign thereto. The output signals are applied to the valve TT whose input circuit is of high impedance while its output circuit is of low impedance and capable of carrving currents which would cause distortion if taken direct from the valve RT. If the voltage 17 and resistance 8 be suitably chosen, distortion due to insufficient abruptness in the lower anode bend of the valve RT can be counteracted. The effect of the latter valve is to square the form of the signals while reversing their polarity, which is again reversed by the valve TT. The arrangement shown in Fig. 5 is such that output signals from the pair of valves RT1, RT2 are zero for a definite range of input signal strengths of either polarity, while they are of fixed strength and reversed in polarity for input signals exceeding the marginal strength. When the input voltage eg is zero, the batterv 22 makes the grid of the valve RT1 positive so that the filament anode resistance of this valve is negligible in comparison with resistances 5, 18. The voltage drop in resistance 5 then balances the voltage 6, and the output voltage e2 is zero. When the input voltage eg is negative and stronger than the voltage 22 the plate current of valve RT1 is stopped and the output voltage e2 becomes that of the battery 6 (positive). When the input voltage eg is positive and stronger than the voltage 3 the anode-filament resistance of the valve RT2 becomes negligible in comparison with the resistance 18 which is thus in effect shortcircuited. The current in the resistance 5, being now due to the batteries 6, 7 in combination, is doubled; the voltage drop in the resistance 5 is therefore doubled, and the output voltage e2 becomes equal in value but opposite in sign to that of the battery 6. The output voltage is therefore zero for input voltages less than that of the batteries 22, 23, while for larger input voltages it is of fixed magnitude, and reversed polarity.