Hi Cruizzer I build a 6m repeater 10 years ago, 2 yrs on air, till lightning bolt toasted it.
First tried spilt antennas. Lousy performance. Tried adding coax 1/4 wave stubs, but were too broad. Then built 6 cavity hybird ring helical in paint can duplexer. Worked, but tuning drifted due to temp change effecting mechanical size and shape of paint can. You could hear them expand and make a boink noise and the tuning was off severely enough to cause high insertion loss. My next effort was the coaxial heliax stubs. 4tx, 4rx, put into a plywood box, and wrapped in aluminum flashing. Stood up vertically. Think of a pack of cigarettes, 2 rows of 4. Worked like a champ with a homebrew dual 5/8 vertical. I used ceramic multi turn trimmers to tune the series coupling, notch depth / width. The lighter the coupling, the sharper the notch, but the less depth. I used same style trimmers to tweak parallel resonance of the stubs. 73 and good luck! Ed N3SDO
