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
 
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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.

73's
Pete N6QW

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