On Wed, 16 Sep 2009 18:45:43 +0100 Peter Restall wrote: > I was playing about with some low frequency crystal filters at the > weekend (60KHz - it's the ongoing epic that is my MSF receiver :) and I > was just wondering if anybody out there has any good sources of > information that they can point me to - specifically LF crystal filters > and their nuances. There's tons of info on the 'net about MHZ region > stuff, including Wes Hayward's articles - all very useful if I was > building a higher frequency filter. I have never heard about 60 kHz crystal filter. I'm quite sure those are "mechanical filters", but not piezoelectric. If I'm not mistaken they have mechanically resonant cavities, and electromagnetic 'launchers', quite low-impedance. Normal crystal have way too high Q to make a practical filter at that frequency (say Q of 40000, would give a filter of only 1.5 Hz!) John -- http://www.piclist.com PIC/SX FAQ & list archive View/change your membership options at http://mailman.mit.edu/mailman/listinfo/piclist