| 摘要 |
306,896. Telefonaktiebolaget L. M. Ericsson. Feb. 27, 1928, [Convention date]. Filter circuits.-Relates to filters in which a section of the band-pass type is linked with one of the band-rejector types in such a way that the input terminals of several such filters can be connected in series while their output terminals are connected in parallel, or vice versa; and consists in a particular choice of dimensions of the impedances z1, Fig. 1, may be connected to a circuit of impedance z2 through a filter comprising a rejector circuit L1, C1, coupled inductively with am acceptor circuit L2, C2. The input and output characteristic impedances are plotted against frequency in Figs. 2 and 3 respectively; thus the input impedance is of the band rejector type, Fig. 2, and falls off rapidly above and below the vertical frequencies, f<1>, f<2>, while the output impedance, Fig. 3, is of the band-pass type, and rises rapidly above and below these frequencies. The condenser C2 may be replaced by two series condensers symmetrically connected on opposite sides of the inductance L2 (Fig. 9, not shown). The transformation ratio of the coupling L1, L2, is adapted to the ratio of the terminating impedances z1, z2, Fig. 1. The rejector side may form part of the plate circuit (Fig. 4, not shown), or grid circuit (Fig. 5, not shown) of a valve, and in this case the internal capacity of the electrodes and the coil L1 is allowed for in the calculation of the capacity C1 or C2. Chain filters comprising sections of the type described may be constructed as indicated in Figs. 7, 8. The transformer may be replaced by an equivalent network as shown in Fig. 10. Where a number of filters is used to connect a single input circuit with a plurality of output circuits, or vice versa, the rejector terminals 1, 1, of the several filters may be connected in series (Fig. 11, not shown), or their acceptor terminals 2 may be connected in parallel (Fig. 12, not shown), the remaining terminals being connected to separate circuits. In each case the impedances, cut-off frequencies and coupling coefficient are related according to a formula given in the Specification.
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