455khz IF Filters Part 4

Ok, so the journey continues, what i did the other night was to redo the motional parameter measurements of the ceramic resonators and plug them into a different program to design the filter called Ladder Filter Crystal Design.



One thing i did this time was to use a larger value for Holder Capacitance, 100pf, as i was informed that ceramics typically have a Cp in the 100 to 200pf range. the design parameters are 4th order Butterworth with 400hz bandpass.


I built the filter on a scrap of board, having drawn the schematic as in the picture last night, but remembering there was a small difference in the values of C1&7 and C3&5 I built the filter using 68pf for C1&7 and 82pf for C3&5 which was backwards to what the program predicted, and 480pf for C2&6, 10pf was used for C4, as per the design.


Filter response was plotted and it actually looks like a filter. The Centre frequency and bandpass are actually close to where they need to be, and this might be something i can tweak now into a usable filter. More work to come, but, i have made some progress.


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