| 摘要 |
The invention relates to a switchable tuned cavity for bandpass filter, especially for duplexer equipping VHF radiotelephony systems, the cavity consisting of an oscillating circuit, in particular of the helix type, tuned to a first frequency. According to the invention, it furthermore comprises at least one second circuit embracing in series a coil 4 coupled to the coil 3 of the oscillating circuit 1, a decoupling capacitor 5 and a diode 6 whose bias is controlled by a DC voltage supply circuit, in such a way that, depending on the bias of the diode 6, the tuning frequency of the cavity is either that of the said oscillating circuit 1 alone, or that determined by the oscillating circuit 1 coupled to the coil 4 of the second circuit. The invention also relates to a radiotelephony transmitter-receiver comprising at least one switchable tuned cavity according to the invention arranged in a bandpass filter whose width is substantially equal to half the pass band to be scanned, the two tuning frequencies of the cavity then being respectively that of the centre of each half of the pass band to be scanned. Application to radiotelephony systems. <IMAGE>
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