I downloaded a 2-meter receiver schematic using an IC for the dual conversion IF strip. The first 10.7MHz IF uses a crystal filter with a terminating impedance of 1800//5pF. The output impedance of the first mixer and the input impedance of the second mixer are 330 Ohms. If the 5pF parallel capacitance of the crystal filter is taken into account, it would seem that an LC L type network would be used to match the filter to the mixers to have the proper response. On the schematic however, the author uses resistors to do the matching not taking the 5pF parallel capacitance into consideration.

Is ignoring the crystal filter's parallel capacitance a good idea or should it be taken into account no matter what?


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