The performance of a modular helical antenna for Alfvén wave heating is analysed in the framework of 1-D cylindrical theory, including finite-frequency (i.e. Hall current) effects. It is shown that modes with either positive or negative helicity can be preferentially excited in the plasma by tilting the antenna with respect to the poloidal magnetic field. Excitation of pure modes, which is crucial for optimizing the power deposition profile, can be achieved with surprisingly small tilt angles.