So i came across this schematic on Ebay for a 40m dc receiver kit, the front end looked nice so i copied it for my own project.
I am assuming that the band pass is transforming impedance also 50 ohm in and 1500 ohm out into the 612 mixer. I built mine for 50 in and out, by replacing the 270 and 18pf caps with 220 and 56pf.
Using my scope and signal gen i tuned the filter for max amplitude on 7.100mhz, and then did a sweep of the filter from 5 to 9 mhz and plotted its response on the graph above. Looked better than I expected.
Here is the filter as built on the board. Followed by a mess of failures where I was trying to add in a preamp that just kept loading up and not doing anything. Such is life.
I suggest getting one of the many filter software programs readily available on the net. I use the Iowa Hills package as a starting point since it does nearly everything I need. Never again will you need to rely on eBay for a filter design. Have a look at some of the uses I’ve made of this software in my projects.
Regards
Richard VK6TT