T9A05

ANTENNAS AND FEED LINES · Antennas: vertical and horizontal polarization, concept of antenna gain, definition and types of beam antennas, antenna loading, common portable and mobile antennas, relationships between resonant length and frequency, dipole pattern

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Which of the following increases the resonant frequency of a dipole antenna?

ALengthening it
BInserting coils in series with radiating wires
CShortening it
DAdding capacitive loading to the ends of the radiating wires

Why A dipole's resonant length and frequency are inversely related: the half-wave length in feet is roughly 468 divided by the frequency in MHz. Cut the wire shorter and the same half wavelength now fits a shorter wave, meaning a higher frequency. So trimming a dipole is how you move its resonance up in frequency.

Watch out Lengthening it, adding series loading coils, or adding capacitive hats at the ends all make the antenna electrically longer, which lowers the resonant frequency. Loading is the standard trick for making a physically short antenna work on a lower band.

Length up, frequency down. 468/f(MHz) = dipole feet. Short wire, high note, like a short guitar string.

HamSandwich explanation, first draft. The question and answers are the NCVEC text.

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