| 摘要 |
<p>1,115,215. Hybrid transformer circuits. STANDARD TELEPHONES & CABLES Ltd. 24 Feb., 1967, No. 8976/67. Heading H4R. The balancing network 4 of a hybrid transformer circuit, Fig. 2, has variable components 6, and 7, which are adjusted by error signals derived from signals from the upper and the lower parts of the frequency spectrum extracted from both the receiving pair 2 and the sending pair 5 so as to eliminate echoes in the sending pair 5 of signals in the receiving pair 2. Signals in the receiving pair 2 are selected by filters 10 and 11 to extract frequencies of respectively 500 and 2000 c.p.s., which, via phase-shifters 14 and 15, operate gates 16 and 17. The gates inputs are derived from the same respective frequency components in the send line 5 selected by filters 12 and 13 which are alternately connected, by the switches 22a and 22b, to the respective gates 16 and 17, the outputs from which drive, via amplifiers 18 and 19, the motors 20 and 21 to control the values of resistors 6 and 7. Only echo signals in send pair 5 due to signals in line 2 will be effective to drive motors 20 and 21 since all other signals will be uncorrelated. Amplifier 23 prevents signals from the two wire line 3 reaching the inputs of filters 10 and 11 since signals from the two wire line in the send and receive pairs would be correlated. In an alternative embodiment the filters 10 and 11 are replaced by oscillators of the respective frequencies 500 and 2000 c.p.s. which alternately feed signals into the line 2 and also supply gating signals to the gates 16 and 17, Fig. 3 (not shown). The system would be energized for a short time at the commencement of each connection.</p> |
