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Old July 15th 04, 02:43 AM
Tom Holden
 
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Default Cascading Cheap Ceramic IF Filters?

I found some old postings that did not go into the how-to of cascading cheap
ceramic filters in order to improve selectivity. I have a few 4-element and
6-element 455kHz filters with which I am experimenting in an IF
downconverter for sound card DSP, specifically for DRM decoding which
requires a nice flat 10kHz bandwidth. I'm wondering if it is not a good
idea to DC couple them directly back-to-back. Should they be AC coupled?
Should there be a terminating resistor to ground or a T-pad at the junction
to provide a more uniform load/source impedance? Or is it best to make up
for the losses and provide the proper terms by putting an active stage
between them than having the gain makeup before or after?

TIA,
Tom