Long Wire Antenna Calculator
Calculate the theoretical and practical starting length for an end-fed long wire antenna based on operating frequency and electrical length.
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Inputs
Live
Math
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Related
Enter parameters and click Calculate to view results
Formula & Theory
λ (m) = 300 ÷ f(MHz), Theoretical Length = λ × Electrical Length, Practical Starting Length ≈ (285 ÷ f) × Electrical LengthThis formula is used to calculate antenna parameters for long wire antenna calculator.
Overview
This calculator determines the theoretical free-space length and a practical starting cut length for a true long wire antenna. A long wire is generally one wavelength or longer and is usually fed from one end through a suitable matching transformer or antenna tuner.
Input Guide
Enter Lowest Operating Frequency, Electrical Length exactly in the units shown by this long wire antenna. Check the operating band, unit prefix, and decimal position before calculating; these are the inputs used by the formula.
- Lowest Operating Frequency — use MHz.
- Electrical Length — use λ.
Output Guide
The results describe the calculated long wire antenna values for the inputs you entered. Check each value against the available space, selected components, feed system, and operating conditions before making a final design decision.
How This Calculator Works
The Long Wire Antenna uses λ (m) = 300 ÷ f(MHz), Theoretical Length = λ × Electrical Length, Practical Starting Length ≈ (285 ÷ f) × Electrical Length. Supply Lowest Operating Frequency (MHz), Electrical Length (λ) in the displayed units, then use the calculated values as the first engineering target for this wire antennas design or analysis.
Design Notes
Unlike resonant dipoles, long wire antennas are not designed for a single resonant frequency. Feed-point impedance, radiation pattern, and efficiency vary with wire length, height, ground conditions, nearby objects, insulation, and the feed arrangement. The calculated practical length is intended only as a starting point before final tuning.
Build and Tuning Notes
Cut the antenna slightly longer than calculated whenever possible. Install it at the intended height and orientation, then tune by trimming or folding back the end while observing SWR or antenna analyzer measurements. Keep the antenna safely away from power lines.
Frequently Asked Questions
How long should a long wire antenna be?
A true long wire antenna is generally at least one wavelength long at the lowest operating frequency. Longer wires produce different radiation patterns and feed-point impedances.
Why are two wire lengths shown?
The theoretical length is calculated from the free-space wavelength (300 ÷ frequency). The practical starting length uses approximately 285 ÷ frequency to account for real-world installation effects such as insulation and end effects.
Does a long wire antenna require an antenna tuner?
In most installations, yes. The feed-point impedance changes considerably with frequency and wire length, so a tuner or suitable matching transformer (such as a 9:1 or 49:1 unun, depending on the antenna type) is commonly used.
How high should a long wire antenna be installed?
Higher installations generally provide better performance. A practical minimum height is roughly 0.1 to 0.25 wavelength above ground whenever space permits.
Alex Warren
B.Sc. in Electrical & Electronic Engineering (EEE)
Alex specialises in antenna design and wave propagation. His expertise helps ensure these calculators present practical RF concepts, useful design estimates, and clear engineering guidance for students, HAM operators, and wireless professionals.