| 摘要 |
459,343. Impedance networks. NAAMLOOZE VENNOOTSCHAP PHILIPS' GLOEILAMPENFABRIEKEN, Emmasingel, Eindhoven, Holland. May 4, 1936, No. 12560. Convention date, July 26, 1935. [Class 40 (iii)] A band-pass filter having variable bandwidth is so constructed as to be free from the defect, shown in Fig. 2a and due to capacity inherent in the coils, which consists in a change in the pass range asymmetrical with respect to the mid frequency fo. The mutually coupled inductances 1, 2, are conductively in series with further inductances 4, 3 respectively, and these are magnetically coupled to the opposite inductances 2, 1. The coupling between the circuits, and consequently the band-width, can be altered by reversing the connections of the subsidiary inductances 3, 4 separately or simultaneously by means of a switch, and in this way three resonance characteristics a, b, c, Fig. 2b can be obtained if the circuits are symmetrical, but the number of resonance characteristics can be increased to four by making the coupling between 1 and 3 unequal to that between 2 and 4. The relative positions of the coils are adjusted during manufacture but thereafter are fixed ; change of band-width does not, therefore, alter the inherent capacitive coupling of the parts, and for this reason the asymmetrical effect shown in Fig. 2a is avoided.
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