GB149331A - Telephone repeating circuit - Google Patents

Abstract

149,331. Western Electric Co., (Assignees of Clark, A. B.). July 31, 1919, [Convention date]. Repeating and amplifying systems.-A telephone repeater has a frequency filter connected in its output circuit, thus removing the necessity for balancing the filter impedances as to the two sides of the line, and also preventing " singing " of the repeater due to want of balance of the line at the higher frequencies, say above 2,200. As shown in. Fig. 1, the telephone line L is bridged by a resistance 2 connected by symmetrical tap connexions to the input transformer 3 of a valve 4. The output circuit of the valve comprises a filter F and transformer 10 having its secondary in the line L. The resistance 2 is connected to the line at symmetrical points on the secondaries of the transformer 10, and the sections of the line L on either side of the repeater are balanced for currents of voice frequency, thus preventing " sing- ing " at these frequencies. For the higher frequencies, " singing " is prevented by the filter F. which may also be arranged to prevent the passage of currents of lower frequency than those required for speech transmission. As the filter is not conductively connected to the line, its impedances need not be balanced; and the same filter impedances will serve for any line, because their values are dependent on the impedance of the remainder of the circuit, i.e. on the impedance of the output circuit of the valve. As this has a comparatively high value, the filter condensers need only be of small capacity. In the modification shown in Fig. 2, the line L is cut and both portions are balanced by networks N. The output circuit of each valve includes a filter F and is inductively connected to the opposite portion of the line. Specification 142,115 is referred to.