In order to connect a 2m/70cm radio and a 1.25m radio to a triband
antenna (2m/1.25m/70cm), one requires a triplexer and diplexer. I'd
like to cut down on the number and size of equipment to do this.

I asked Comet about making a single compact unit that takes 2m/70cm on
one port and 1.25m on the other. Mick Stwertnik told me that they
designed and specced it out, but the cost would be a prohibitive
$200-ish.

So I investigated making my own and found Jim Tonne's Diplexer program.
I asked him if he could extend the program to allow for designing
triplexers. He had some hackish solution that sort of worked, but he
doesn't know the math to do it correctly in the first place.

Where should I go from here?

--
David Griffith
--- Put my last name where it belongs