Patent GB-420595-A (GB)
Title: Improvements in electrical two-way amplifiers
IPC: H04B3/38
Filed: 1933-03-31
Abstract: 420,595. Two - way transmission. TELEFONAKTIEBOLAGET L. M. ERICSSON, 33, Kungsgatan, Stockholm. March 31, 1933, Nos. 9791 and 9792. Convention dates, Aug. 5, 1932 and Nov. 14, 1932. [A Specification was laid open to inspection under Sect. 91 of the Acts, Oct. 2, 1933.] [Class 40 (iv)] Two - way audiofrequency amplifying systems in which different frequencyranges are employed for the two directions of traffic are provided with a single amplifier for both directions, the signals being routed by means of networks of the kinds described in Specifications 369,984 and 417,386. Such a network comprises a Wheatstone bridge having two arms or two diagonals formed by two filters which have the same pass band but are inverse to one another. The bridge N, Fig. 1, having inverse filters F1, F2 in adjacent arms, is substantially balanced for frequencies lying within the passband common to the filters. These frequencies therefore pass from l1 to l2 by way of the filters F1, F<1>1 and F2, F'2, the bridge N<1> being similar to the bridge N. For frequencies lying outside the pass band the bridges N, N<1> are unbalanced and these frequencies are routed through the amplifier W. The two pairs of filters F1, F<1>1 and F2, F<1>2 may be replaced by two single filters (Fig. 2, not shown). In another arrangement, Fig. 4, the network M is constructed as shown within the rectangle M in Fig. 3. Two bridges N, N<1> have their filters F, F1 in common. The resulting network acts as a band pass filter between terminals a and b<1>, and between band a<1>; it acts as a bandsuppression filter between a and b, and between a<1> and b<1>; and transmission is blocked for all frequencies between a and a<1> and between band b<1>, the pass frequencies being eliminated by the bridge effect while the remainder are eliminated by the filter effect. Thus one range of frequencies S1 may pass from line l1 to line l2, Fig. 4, via terminals b<1> and amplifier W, while the remaining frequencies S2 pass directly between terminals band a. Frequencies S1, passing from b to a<1> are dissipated in a resistance R, but this waste of energy may be checked by a filter inverted at b. The amplifier W may be transferred to the side a, a<1> of the system (Fig. 5, not shown). Two such arrangements may be combined to form a two-way amplifier, Fig. 6, for amplifying a frequency band S<1> in the left-to-right direction and a band S2 in the opposite direction. The bands S1, S2 either follow the course shown by the arrows or pass in the reverse direction (Fig. 7, not shown). Waste of energy in the resistances R may be prevented by insertion of filters. By the use of four bridges and one amplifier, two-way amplification for each of the frequency bands S1, S2 is obtained (Fig. 8, not shown). The Specification as open to inspection under Sect. 91 comprises also arrangements in which (i) one leg of each of two lines goes direct to the amplifier (Figs. 1, 2, 4, 5, Cancelled, not shown) ; (ii) the two lines are directly connected to one another, the amplifying network being coupled across them (Fig. 6, Cancelled, not shown) ; and (iii) the scheme of Fig. 3 is modified, one terminal each of pairs a, a<1> being connected to a corresponding terminal of pairs b, b<1>. This subject-matter does not appear in the Specification as accepted.