| 摘要 |
1349091 Filters GEC-GENERAL SIGNAL Ltd 14 Feb 1972 [12 Feb 1971] 4540/71 Heading H3U A bandpass or frequency selecting filter comprises cantilevered, and fixed, nickel-iron alloy reeds 10, 26 forming cores for input windings 18, 20 having equal numbers of turns and inducing similarly directed flux in the reeds. The output circuit comprises coils 28, 30 connected in opposed phase senses, having equal numbers of turns, and magnetically coupled via reeds 10, 26 to coils 18, 20. When the input frequency substantially coincides with a flexural resonant frequency of reed 10, the latter, due to interaction of its induced magnetism with permanent magnet 14 vibrates, increasing the effective impedance of coil 18 and thus causing an imbalance between the voltages across coils 18 and 20, leading to an output at terminals 32. A component of such output is provided by generator action of coil 28; due to the varying reluctance of the magnetic path between reed 10 and magnet 14. As frequencies removed from resonance, the device is balanced, and no output is obtained. All coils may have an equal number of turns. The filter may be employed in the feedback loop of an oscillator, and receiving and transmitting oscillators of such type may be used in track circuit railway signalling systems of the type disclosed in Specification 869,896, operating at a specific frequency. |
