IF crystal filter having a selectively adjustable frequency response

摘要

An IF crystal filter for a VHF receiver including:P Pa crystal filter (18) having an input (22) and an output (24) P Pa reactive impedance means (26) coupled across the crystal filter input and output for changing the selectivity characteristics of the crystal filter by a predetermined amount; andPP switching means (32) having a control input responsive to a control voltage, and coupled to said reactive impedance means for selectively shunting the reactive impedance means to ground, whereby to change the selectivity of the filter.