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collection of quartz crystal ladder filters
in my designs i mostly use 6 pole crystal ladder filters built with standard available quartz crystals. since the price of standard available crystal units is relatively low and since the tests show, that 6 quartz crystal are just the right number to effectively and radically filter out the opposite side band in a ssb receiver, i don't see any reason why to built filters with less crystal units. 6-pole crystal filter is also not to sensitive regarding component parameter variations. i use 5% np0 (cgo) ceramic capacitors and an f-meter with 10 hz resolution + simple quartz oscillator to select the crystal units with resonant frequencies as close to each other as possible. the resonant frequency deviation between the units should not be bigger than 20 .. 30 hz to get best results. the units with bigger deviation could still be used in bfo oscillator.
