Re: Crystal ladder networks
As noted, the terminating-impedances of these filters are very important. In your design you've got a parallel resistor terminating the input, but this is shunted by the winding of your transformer, which will present a reflected version of the mixer-output-stage's impedance in parallel with your shunt-resistor.
When I've built these sorts of filters I've usually driven them from an emitter-follower, whose emitter-resistor has a value to present the 'right' load to the filter input.
At the output-end, I use another emitter-follower - the trick here to present the 'right' impedance is to provide base-bias to the emitter-follower by using two identical resistors in series, each of 2x the reaquired impedance - the centre-point then sits at 1/2 ths supply voltage and also presents a good match to the filter's output.
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