| 摘要 |
A signal coupler includes a transformer having a primary and a secondary winding. Each transformer winding has a pair of associated winding terminals and is also split at an intermediate winding position to form a pair of supplemental winding terminals. Circuitry is provided between each pair of supplemental winding terminals so as to provide different impedances in different frequency bands. In particular, a first circuit, which provides a first impedance in a first frequency range, is connected across the supplemental winding terminals of one winding. A second circuit, is connected across the supplemental winding terminals of the other transformer winding. This second circuit, in combination with the first, provides a second impedance in a second frequency range. In the disclosed embodiment, the first circuit provides an impedance of 600 ohms in the voiceband frequency range. The second circuit in combination with the first provides an impedance of 100 ohms in a frequency range extending above 40 kHz.
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