Patent GB-266458-A (GB)
Title: Improvements in voice-operated relay systems
IPC: H04B3/20
Filed: 1925-11-26
Abstract: 266,458. Standard Telephones & Cables, Ltd., (Western Electric Co., Inc.). Nov. 26, 1925. Repeating and amplifying system.-Relates to voiceoperated switching devices for suppressing echo and singing effects in the terminal apparatus connecting a radio receiving and transmitting station T, R with associated land lines ML and consists in the provision of means for enabling this type of apparatus to function efficiently under the control of modulated high-frequency energy of the form shown in Fig. 4 in which the corresponding rectified voice currents, Fig. 5, may fall periodically e.g. between the points 2, 3 and 6, 7 below a minimum operative value Z. As shown in Fig. 2, signal currents on the way to the transmitter T are rectified in a shunt circuit comprising a rectifier R, the output of which flows through the coils O1, 02 of two polarized relays PR1, PR2. When the armature of relay PR1 moves over to its front contact. the echo-suppressor apparatus R1 &c. associated with the receiver line LW, together with the line LW, are short-circuited by the bridge line 12. When the relay PR2 is energized through the winding 02 it removes a short-circuit from the relay RT, which then open-circuits the bridge line 11 and so renders the transmitter T operative. Simultaneously the relay PR2 energizes two slowrelease relays EHO and VHO. The echo hangover relay EHO closes an auxiliary bridge-line 14 to maintain the line LW disabled for a definite time after the voice currents have ceased, whilst the voice hang-over relay VHO opens a short-circuit about the relay RT, independently of the relay PR2, and so similarly maintains the bridge line 11 open-circuited for a definite time after the voice currents have ceased. Locking the relay PR1. If the available current energy falls below the level Z, Fig. 5, the armatures of the relays PR1, PR2 may fall back and undesirable results will ensue. To prevent this an auxiliary winding L1 is provided to lock the armature of the relay PR1 against its front contact, once it has moved over to that position. The coil L1 is energized over either of two paths, one controlled by the contact of a slow-operating relay CHO through resistances 15, 16, and the other a parallel path through resistances 15<1>, 16<1>. Both paths are short-circuited when the armatures of PR1 and PR2 are against their back contacts. If, however, either is moved on to the front contacts, a current will flow through the coil Ll tending to throw the armature of PR1 on to its front contact. This movement simultaneously removes a short-circuit from the relay CHO, which allows the winding L1 to be energized even if the parallel path through 15<1>, 16<1> is broken by the falling-back of the armature of PR2. Sequence of operations. Referring to Fig. 5, the pulse of current received between the points 1, 2 is sufficient to bring the winding L1 into operation and so lock the relay PR1 against its front contact during the period of low current amplitude 2 to 3. From the point 4 the relay PR2 is held against its front contact and the relays EHO and VHO are energized, and remain so until a definite period after speech has finished, so that no echoes can be returned through the receiving channel LW. During reception the transmitting line LE is disabled in a similar manner through a bridge circuit containing a rectifier R1 and associated apparatus. Modified locking arrangement. In an alternative form the winding L1 is connected across the neutral points of a Wheatstone resistance bridge, one of the arms of which comprises the winding of the slow-release relay CHO. When either of the relays PR1, PR2 is actuated, the bridge balance is upset and the relay CHO is operated to energize the locking-winding L1 as before.