you don't need a balun for that. just connect the center lead to one half of the dipole, and the shield to the other half of the dipole. baluns (even 1:1 baluns) will introduce losses. a dipole is "balanced" even if fed with coax. all you need to concern yourself with is making sure the dipole elements are 1/4 wavelength, and the total length is 1/2 wavelength. for 1/2 wave in meters the formula for a wire antenna is 143/f, and each element is 1/2 that length. so a wire dipole for 100Mhz would be 1.43 meters, and each of the two elements would be 71.5cm. (this takes into account the 95% velocity factor of wire)