| 摘要 |
To provide a low pass filter (10) with good harmonic rejection and minimal insertion loss, a relatively low impedance (L6) is selectively switched in parallel with a shunt impedance (L3) located in a network of the filter (10), whereby the series resonant frequency provided by the shunt impedance in combination with a relatively high impedance point is altered and the filter characteristic is changed; whereby the passband is selectively widened and narrowed whilst stopband rejection is kept below a specific level thereby filtering out harmonics in the stop band. In a radio communications transceiver, Fig 4, not shown, a microprocessor (48) is used to control the switching voltage Ux in response to a transmission frequency. <IMAGE>
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