SDH is a robust folded dipole of exceptional bandwidth suitable for mounting on the side of a mast tower. Electrical connections are fully sealed. The integral balun minimizes interaction between antennas on the same mast and prevents distortion of the polar diagram by feeder radiation. Two or four SDH dipoles can be stacked vertically and fed in phase to give all-round gain of 3db or 6db respectively. Due to the wide bandwidth characteristics of this antenna it is possible to use one antenna for both transmitting and receiving without introducing any loss. The received signal response of type SDH is flat to more than 20% of the centre frequency.