| 摘要 |
1508714 Tunable band-stop filters PHILIPS ELECTRONIC & ASSOCIATED INDUSTRIES Ltd 1 April 1976 [4 April 1975] 13167/76 Heading H3U [Also in Division H1] To avoid variation of the suppressed frequency when the amount of suppression is adjusted in a band-stop filter circuit, Fig. 1, a coupling inductor 7 and a compensation inductor 19 are movable simultaneously relative to a tuned-circuit inductor 15 by a drive mechanism 43, 41, Fig. 4, so that an increase in the coupling between inductors 15 and 7 is accompanied by a decrease in the coupling between inductors 15 and 19, and vice versa. As shown in Fig. 1, inductor 7 has a centre tapping 11 connected to a shunt arm impedance 13, e.g. parallel-connected capacitor 45 and resistor 47, Fig. 4, and compensation inductor 19 is shortcircuited. The filter is tuned by a variable capacitor 17 in series with inductor 15. The drive mechanism comprises a rotary shaft 43 carrying an eccentric disc 41 which engages both inductor 19, which is constituted by a resilient wire, and an adjusting screw 39 for inductor 7, which is constituted by a spring-biased metal strip, so that upon rotation of shaft 43 one of the inductors 7, 19 approaches inductor 15 while the other is moved further away. An alternative arrangement in which inductors 7, 19 are fixed and inductor 15 is movable is also envisaged. A fine adjustment of the frequency of the tuning-circuit may be effected by rotation of a metal plate 53 on a shaft 55 to vary the inductance of inductor 15.
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