since I’m thinking about upgrading my ground station with a 70cm antenna,
I decided try designing an antenna diplexer.
After some googling for existing schematics I came across the micro-diplexer by kw4fb, which has some really nice component values allowing it to be build from SMD components without winding your own inductors.
I took the design, added a lowpass filter to the 2m branch to get rid of some the strong FM broadcast stations in my area and plugged it into QUCS.
After some tweaking I ended with the following characteristics:
The passbands could be a little closer 0dB, but since I need two LNAs in front of it anyway I decided not to worry to much about it.
After @pjm’s suggestion in the IRC channel I decided to add two bias-tees for the antenna inputs and designed a first PCB in KiCad.
The layout is not yet final.
It certainly lacks a bunch vias connecting the ground planes.
The dimensions of the board should fit a cheap aluminium housing I got from ebay some time ago.
(I know something ferromagnetic might be better, but on the other hand my SDR wrapped in plastic.)
I don’t have to much experience with designing PCBs for radio stuff,
some helpful comments and tips would be highly appreciated.
I think the trace connecting the output and the 70cm filters diagonally across the board looks a bit odd and might be to close to the power supply trace.
Also I’m not to sure about the way the two traces meet at L1.