| 摘要 |
Channel preselection filter with capacitive coupling between a primary tuned circuit 20, 21, 22, 23, and a secondary tuned circuit 30, 31, 32, 33. Filter characterised by the presence of variable-capacitance diodes 21, 31 for tuning the primary and secondary circuits and associated with two other variable-capacitance diodes 40, 41, mounted in opposition, which produce the capacitive coupling and are controlled simultaneously with the tuning diodes 21 and 31. Adjustment of the coupling factor in the high portion of the frequency band can be achieved with a fixed capacitance 50 or 51 as required. Application to the preselection of channels for television receivers, in particular suitable for receiving an extended VHF band. <IMAGE>
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