The 20 Meter Band Pass Filter and SBL-1 Receiver Mixer

The Receiver Band Pass Filter is also duplicated for the the Transmitter insofar as values are concerned. The Receiver BPF used 25 Turns of #28 on a T-30-6 iron powder core (this is 2.28 uHy) and four 0-50 PF trimmers were used for the main capacitors and a 1 PF NPO was used for linking the sections. The filter was set for 14.2 MHz and the four trimmers peaked for maximum signal . Thus the values can be precisely set for 14.8 PF and 39 PF as shown in the schematic below:



Noteworty is that I saw a you tube video about the need in Band Pass Filters to isolate the sections to avoid coupling at frequencies (ie harmonics) other than the design frequency and so in the photo below you will see a shield that was installed bewteen the two sections. I use galvanized sheet metal that can be purchased in small sheets from Home Depot. The good news is that you can solder to the metal, it is easily cut with "tin snips" and is easily bent with a pair of hand pliers. I used a scrap piece and there was a hole drilled along one edge and that hole has no purpose. The way I made the shield was to cut a "u" shaped notch at the bottom so it would just clear a solder pad but the ends haveing more material were simply soldered to the PC Board.