Hi Joe, >The best PL filter I ever saw was one I built out of a digital SCF design a couple of years ago. >I realize that the paper is referencing commonly available products, but I wish someone >would make this thing up for sale. > >Here is a link to the data sheet: > >http://www.mix-http://www.mix-http:/ To make a standalone CTCSS removal filter you'll need the SCF and a clock source. To be safe, I'd also add an antialias lowpass filter ahead of the SCF (it's a sampled-data device) and a smoothing filter after the SCF (to remove the stairsteps from the resulting sampled waveform). The part you mention is available in both 100 and 1000 clock-to-corner ratios, and presumably the sampling is fast enough to not cause problems in a narrow voice passband, but I'd overengineer it anyway. We use an MF6 lowpass SCF in the 6K and 7K controllers to turn digitally-generated tone square waves into sine waves. The MF6 has extra op amps built in that can be used for the pre- and post-SCF filters. 73, Bob, WA9FBO
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