Free Half-Wave Dipole Antenna Calculator
Calculate exact physical antenna wire lengths, quarter-wave radiator legs, end-effect velocity reduction, and feedpoint impedance.
📡 Frequency & Antenna Wire Specs
📊 Antenna Cutting Dimensions
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How Half-Wave Dipoles Work
The half-wave center-fed dipole is the fundamental reference standard for all radio antennas. It consists of two equal collinear conductors, each approximately one quarter-wavelength ($lambda/4$) long, fed at the center where RF current is highest and impedance is lowest.
The Standard Dipole Formulas
Why PVC Insulated Wire Cuts Shorter
Bare copper wire traveling through air operates with an end-effect velocity factor $k approx 0.95$ to $0.96$. However, ordinary hardware store insulated stranded hookup wire (such as THHN or PVC insulated wire) has a dielectric coating with a higher dielectric constant ($ arepsilon_r approx 3.0$). The dielectric slows down RF wave velocity along the copper surface, requiring the physical wire to be 2% to 4% shorter to resonate at the exact same operating frequency.
Frequently Asked Questions
Why is the formula 468/f instead of 492/f?
In free space, half a wavelength in feet is 492 / f(MHz). However, real-world practical antennas experience two effects: capacitance at the open ends of the wire (end effect) and the ratio of wire diameter to length. These factors slow down the electromagnetic wave by approximately 5%, reducing the physical resonance length constant from 492 down to approximately 468.
How does an Inverted-V configuration change impedance?
When you drop the ends of a horizontal dipole down at a 90° to 120° angle (an Inverted-V), the capacitive coupling between the two wires increases, dropping feedpoint radiation resistance from roughly 73 ohms down to 50 ohms. This provides an almost perfect native 1:1 match to standard 50-ohm RG-8X or RG-213 coaxial cable.
Should I always cut the wire slightly longer than calculated?
Yes! Always add 6 to 12 inches (15 to 30 cm) to each leg when cutting your initial wire. It is vastly easier to fold back or trim a few inches of copper wire during SWR analyzer tuning than it is to solder on extra wire if your antenna resonates too high in frequency.