In a CATV housing the main RF circuit, a coupler circuit and splitter circuit are located respectively on a platform board, coupler board and splitter board respectively. The coupler board is between and perpendicular to the platform board attached to the housing and to the splitter board attached to the lid. The coupler circuit has a main RF circuit input and output near the bottom of the coupler board and a tap output to the splitter at the top of the board. A ground plane on the coupler board approximates, relative to the coupler circuitry, transmission line impedance. In combination with ground planes on the platform board and splitter board, the ground planes provide approximate transmission line impedance to both the main RF path and to the path through the coupler to the splitter output.