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Guy Insulator Capacitance

March 5th Fact-of-the-Day

It is well known that antenna tower metallic guy cables should be separated into non-resonant lengths by means of insulators to avoid antenna radiation pattern distortion, frequency detuning, symmetry imbalance, feed impedance change, and other problems that resonant conductors near an antenna can cause. However, the effect of guy insulator capacitance is often overlooked. A long conductor that is separated into sections by insulators is only truly separated at radio frequencies if the insulators have no capacitance. All insulators have capacitance. Therefore, a long metallic guy cable that appears to be broken into sections by insulators is in reality a long conductor with series loading capacitors. Series loading capacitors raise the resonant frequency of a long conductor by an amount that depends on their number, spacing, and individual capacitive reactances. The resultant resonant frequency is not the resonant frequency of the individual sections as is usually assumed. ©2005 Martek International All rights reserved.

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