Top loading of monopole antennas can improve their efficiency and impedance characteristics. The use of portions of an upper level of guy wires on guyed towers can provide increased base resistance but does not necessarily improve horizontal plane efficiency at MF. At lower frequencies the increase in base resistance from guy wire top-loading can benefit efficiency as radiation resistance of he monopole declines with decreased electrical length. Horizontal “wheel” or “cross” top loading is effective so long as it is sufficiently dense so as to increase capacitance to ground substantially.

This presentation will show the effects of various types and amounts of top loading. Because AM station antenna site availability has become more limited, shorter antenna towers with top-loading at new or modified sites can sometimes be beneficial.