Calculator Inputs
Formula Used
Wavelength: λ = c / f
Ideal element length: Lideal = λ × electrical fraction
Corrected physical length: Lcorrected = Lideal × velocity factor × end-effect factor
Examples: Quarter-wave = 0.25λ, half-wave dipole = 0.50λ, 5/8-wave = 0.625λ, Yagi driven element ≈ 0.475λ.
This calculator uses the speed of light in free space for wavelength, then applies user-selected adjustment factors. Final field tuning is still necessary because support structures, feed systems, conductor thickness, insulation, and nearby conductive objects can change resonance and impedance.
How to Use This Calculator
- Enter the operating frequency and choose its unit.
- Select the antenna model you want to size.
- Set velocity factor if your conductor or system needs it.
- Enter an end-effect correction percentage for a practical cut length.
- Choose the output unit for fabrication or workshop use.
- Press the calculate button to view the result above the form.
- Review comparison values, graph trends, and design-specific details.
- Download the result table as CSV or PDF if needed.
Example Data Table
| Frequency (MHz) | Wavelength (m) | Quarter-Wave (m) | Half-Wave (m) | Full-Wave Loop (m) |
|---|---|---|---|---|
| 3.5 | 85.66 | 21.42 | 42.83 | 85.66 |
| 7.0 | 42.83 | 10.71 | 21.41 | 42.83 |
| 14.2 | 21.11 | 5.28 | 10.55 | 21.11 |
| 28.0 | 10.71 | 2.68 | 5.35 | 10.71 |
These values are illustrative starting points. Actual cut lengths often need trimming during real installation and measurement.
Frequently Asked Questions
1) Why does the physical antenna differ from the ideal wavelength fraction?
Real conductors, insulation, nearby objects, and antenna thickness shift resonance. That is why practical antennas are usually shortened slightly, then trimmed during testing for the final resonance point.
2) What velocity factor should I use?
Use 1.00 for a free-space estimate. Lower values are useful when material properties or design assumptions effectively shorten the required physical length.
3) Is the 95 percent correction always correct?
No. It is a common starting point, not a universal rule. Final adjustment depends on conductor diameter, insulation, mounting height, and nearby structures.
4) Can I size dipoles and monopoles with this page?
Yes. The calculator includes quarter-wave monopoles, half-wave dipoles, single dipole legs, full-wave loops, 5/8-wave verticals, and approximate Yagi element lengths.
5) Why are Yagi values marked as approximate?
Yagi design depends on boom spacing, element diameter, number of directors, desired gain, and target impedance. These values are solid first-pass estimates, not a replacement for detailed optimization.
6) Does this calculator include feed-point matching?
No. It focuses on element length estimation. Matching networks, baluns, stubs, gamma matches, and feed-line effects should be designed separately.
7) Which output unit should I choose?
Choose the unit that matches your workshop tools. Meters work well for general design, while feet and inches are useful for fabrication and field cuts.
8) Should I trust the graph for exact construction lengths?
Use the graph to understand trend behavior. It is excellent for planning, but final build dimensions should still be confirmed by measurement and tuning.