Friday, November 25, 2016

FPM5 Band Pass and Low Pass Filter Boards

Failure into Success!!!!

Having a CNC Milling machine in one's garage is a blessing and a curse! I built two new boards after a quick design using G Simple only to discover I made a serious errors on the BPF and LPF boards for the FPM5. On prior similar boards there was a continuous ground plane something which I forgot when I redesigned the two boards and now I had many isolated islands which should have been part of the topside ground plane. The blessing is that you can make boards quickly --the curse you might have to redesign the board.
Well enter innovation and my resolution was that I connected the isolated islands to a common ground plane on the bottom side and thus won't have to remake the boards. Today I completed three bands of the BPF and two band on the LPF. These can be seen on the photo below. The 42IF123 transformers do not work too well as a 75M BPF and so this filter was built using discrete components. The filter was 1st simulated in  LT Spice and then built
The BPF is on the left and the LPF on the right. The screws going down the middle connect the islands to a common ground plane.

This seems to have resolved the problem --when I get it reinstalled we'll find out for sure.

Pete N6QW