T9A08

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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Why is a 19-inch-long vertical antenna often used on 2 meters?

AIt has high gain
BIt is a resonant half-wave
CIt is a resonant quarter-wave
DIt has low RF radiation exposure

Why A quarter-wave vertical is the standard mobile/handheld whip because it works against a ground plane (the vehicle roof or radio chassis) to act like half of a dipole. The quarter-wave length in feet is roughly 234 divided by the frequency in MHz, so at about 146 MHz that is 234/146 = 1.6 feet, or roughly 19 inches. At resonance the antenna presents a near-resistive, low feedpoint impedance that matches 50-ohm coax well.

Watch out A resonant half-wave on 2 meters would be about twice as long, roughly 38 inches; a 19-inch whip is half of that. And a simple quarter-wave whip has essentially no gain over a dipole.

Quarter-wave feet = 234/f(MHz). 234/146 = 1.6 ft = 19 inches. Half-wave would be 38.

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

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