EMRFD Message Archive 5028

Message Date From Subject
5028 2010-09-03 12:04:35 Phil Sittner Crystal Resonator Filters
I've been doing some experimenting with 429khz ceramic resonators picked up at a swap meet. I thought it would be interesting to measure their parameters and build a 4 pole filter and see how it tracks with the calculated performance in ladpac. A 20-piece sampling yielded resonances between 415.060 and 416.734 khz; Q's ranged from 1819-3355; L averaged 55.6uH and Cf averaged 26.4pF. A four pole was designed and built which closely matched the ladpac model; insertion loss measured 3.3dB (model showed 2.86), filter center measured 416.77khz (model predicted 416.7) and the bandwidth was at the 2khz specified. My next attempt was to raise the center frequency to match the LO frequency of 429khz and this is where I ran into trouble with insertion losses rising to 11dB after shifting the bandwidth by 6.3khz. Ladpac predicted an additional loss of only a couple of tenths of a dB. The other option is to shift the LO oscillator down to the filter frequency but I don't know how to accomplish that. Does anyone have a suggestion as to how I might go about getting these two frequencies to match up?

Phil kd6rm

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