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A knowledge of the radio-frequency voltages on the insulation of broadcast tower antennas is important to the design engineer, since a too-large factor of safety may add unduly to the tower cost. Attention is first given to the base-insulator voltage. The magnitude of this voltage is also of interest in the design of lighting chokes and coupling equipment. Theoretical values are derived and shown in curveform as a function of antenna height. The theoretical curves are supplemented by experimental data taken on self-supporting tapered towers, guyed cantilever towers, guyed uniform-cross-section towers, and guyed tubular steel masts. A theoretical treatment is then given concerning the role of guy wires from an electrical standpoint. Consideration is given to the currents in the guys, and the voltages on the guy insulators. Measurements are presented of the voltages existing on the guy insulators of two guyed masts of different constructions. These voltages are found to be so small that there seems little need for elaborate insulation except for the presence of high static or induced lightning voltages. The paper is concluded by some considerations of ways of providing protection against these high instantaneous and random voltages without the use of expensive and elaborate insulation.