| 摘要 |
A high pass coupler or filter network provides a bypass for relatively high frequency AC signals, while providing DC signal isolation and avoiding loading the track for relatively low frequency AC signals, around a set of insulated joints in a railroad track or the like. The high pass coupler includes a coupling portion for connection to a track and a dynamically resonant filtering portion with a selectable low cut off frequency determined by the proper size capacitor. The capacitor sets up resonance with the track inductance, which decreases in magnitude in response to the moving shunt affect of a train approaching the coupling portion and thus increases the resonant frequency of the coupler, and the capacitor is of a magnitude that ensures the coupler resonant frequency will not exceed the frequency of the AC signals normally to be passed by the coupler. Moreover, in the high pass coupler, losses may be introduced, for example, by a potentiometer to present to the coupled AC signals and particularly to the system employing the same an impedance characteristic at least approximately equivalent to the normal track impedance characteristic presented thereto if the track were electrically continuous.
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