From: http://vk4ffab.info/2016/10/20/9mhz-if-filter/ After having lots of success with DC receivers, i guess the next logical step is to move to a superhet design. So time to start playing with crystal IF filters. Everything starts with a schematic, no i did not design the filter using software, nor did i measure the emotional parameters of the xtals to match them up, just went hit and miss to see what happens. I made 2 identical filters, one with the 100pf caps and another with 50pf caps. Went with the super ugly design method on a scrap of board thats been used far to many times for other experiments. Using the lowest output setting on my signal generator, a series of measurements were made, converting the amplitude millivolts to Db and each filter was plotted and graphed in a spread sheet. 1oopf cap version, data below -45db is not all that accurate as my scope was picking up general rf noise to the tune of 10mv, filter is about about 900hz wide. this was graphed prior to terminating the filter with 1K impedance, so it might be a bit wrong town, its something i will have to redo. Next job is to measure some parameters of the crystals and then use Dishal to give me better cap values and to built it again, to see if I can make it better with much less ripple and with more theoretical shapes.