A four element Yagi Antenna for 50 MHz band.
The reflector and the director elements can be mounted directly to the metallic boom, while the Driven element must be insulated from the boom.
The driven element is basically a simple folded dipole and foreseen a 4:1 balun. Usage of a folded dipole as driven element of the yagi antenna is almost common on VHF Yagi designs since it allow broading the SWR bandwidth.
If the broading is not so much important, the antenna can be directly feeded with a conventional dipole directly connected to a 50 ohms coax cable.