Initially these were down at the “classic” IF frequency, 455KHz. You needed crystals spaced a certain amount apart, and since one section usually wasn’t good enough, you needed two crystals per frequency. When SSB started becoming popular in the fifties, something better was needed, so the half-lattice filter became common. To make it wider, it was loaded down with resistors. Very selective, but not great skirt selectivity. Posted in hardware, how-to Tagged crystal oscillator, pcb, RF, xtal Post navigationįor a long time “crystal filter” meant a single crystal. Thanks to Dangerous Prototypes for the tip. If you aren’t familiar with Spice simulation you can get caught up by checking out the series of Spice articles by our very own. also walks you through the software simulation process using LTSpice. goes into detail about the software he uses and some of the applications of crystal ladder filters.īPF designed by The process includes measuring individual xtals to determine which ones will work together for your target frequency. Which you can find much more in-depth information regarding the design of a xtal BPF. ’s schematicOne of the sources that cites is ’s personal site which is primarily dedicated to amateur radio projects.
If you want a set of these purple PCBs you can order them straight from the purple fab. explains his crystal ladder design on his blog and links to several sources for understanding the theory and creating your own crystal ladder band pass filter. A less common use would be to make a bandpass filter (BPF) for an RF signal. Most hobbyists use crystals as an external clock signal for a microcontroller.
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