| 摘要 |
In a frequency demodulator, device for improving the signal/noise ratio comprising a passive bandpass filter composed of a fixed filter and of a filter which can be adjusted through a control circuit, the said device being such that the adjustable filter is symmetric and comprises two coupled resonators 30 to 34 and 50 and 54 with adjustable resonant frequency and such that the control circuit comprises means of continuous adjustment of the said resonant frequencies. Preferably, each adjustable resonator comprises at least one inductor and one or more capacitors associated with a varactor diode, these diodes being mounted head-to-tail with one another and the control circuit is connected to each adjustable resonator in such a way that the variation in electrical magnitude thus controlled increases the capacitance of one of the adjustable resonators and reduces that of the other symmetrically. Application: receivers of television programmes broadcast by satellite. <IMAGE>
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