Calculator
Example Data Table
| Band | Frequency MHz | Driven Factor | Parasitic Factor | Spacing Factor | Use Case |
|---|---|---|---|---|---|
| 2 Meter | 146.000 | 0.475 | 1.050 | 0.150 | Portable VHF antenna |
| 6 Meter | 50.125 | 0.475 | 1.045 | 0.160 | Weak signal work |
| 70 cm | 435.000 | 0.470 | 1.040 | 0.140 | Compact UHF antenna |
Formula Used
The calculator starts with wavelength. The basic formula is wavelength equals 300 divided by frequency in MHz.
Wavelength: λ = 300 / f
Driven element: Driven length = λ × driven factor × velocity factor.
Parasitic element: Parasitic length = driven length × parasitic factor.
Spacing: Element spacing = λ × spacing factor.
Boom length: Boom length = spacing plus selected boom allowance.
A reflector is usually longer than the driven element. A director is usually shorter. Adjust the parasitic factor to match your chosen design.
How to Use This Calculator
- Enter the operating frequency in MHz.
- Select driven plus reflector or driven plus director.
- Choose metric or imperial output.
- Enter the velocity factor for your element material.
- Change the length and spacing factors if needed.
- Press the calculate button.
- Cut each element carefully using the displayed half side lengths.
- Export the result with CSV or PDF buttons.
Article: Designing a 2 Element Yagi Antenna
Simple Directional Antenna Planning
A 2 element Yagi antenna is a useful directional antenna. It has one driven element and one parasitic element. The parasitic element can be a reflector or a director. A reflector is placed behind the driven element. A director is placed in front of it.
Why Element Length Matters
Element length controls resonance. A small error can shift the useful frequency. This is more visible at higher frequencies. Always measure carefully. Use the calculated value as a starting point. Then trim slowly while testing the antenna.
Understanding Spacing
Spacing changes gain, impedance, and front to back ratio. Close spacing can improve compactness. Wider spacing can change the feed point behavior. Many simple two element designs use spacing near 0.1 to 0.2 wavelength. This calculator lets you set that value.
Reflector and Director Choices
A reflector is normally longer than the driven element. It pushes energy forward. This gives better rejection from the rear. A director is usually shorter. It pulls radiation toward the forward direction. Both styles can work well for small stations.
Construction Notes
Real antennas need final adjustment. Tube diameter, clamps, feed line, nearby metal, and mounting height affect results. A split driven element may need an insulator at the center. A coax choke near the feed point often improves current balance.
Practical Testing
Use an antenna analyzer when possible. Check the lowest standing wave ratio near your desired frequency. If resonance is too low, shorten the driven element slightly. If resonance is too high, lengthen it if possible. Make small changes only.
Best Use
This tool is best for quick planning, rough cutting, and learning. It is not a full electromagnetic model. Still, it gives useful dimensions for hobby builds, field antennas, and educational work.
FAQs
What is a 2 element Yagi antenna?
It is a directional antenna with one driven element and one parasitic element. The parasitic part may be a reflector or director.
Is the reflector longer than the driven element?
Yes, a reflector is usually longer. It is often about three to six percent longer than the driven element.
Is a director shorter than the driven element?
Yes, a director is usually shorter. It helps pull the radiation pattern toward the forward direction.
What spacing should I use?
Many small two element antennas use spacing between 0.1 and 0.2 wavelength. Testing helps find the best point.
Why is velocity factor included?
Velocity factor adjusts the physical length. Real conductors and construction details can make the ideal length slightly different.
Can I use this for VHF and UHF?
Yes, the calculator works for many frequencies. Higher bands need more careful measurement because errors become more important.
Does this replace antenna modeling software?
No. It gives practical starting dimensions. Full modeling software gives deeper pattern, impedance, and current analysis.
Should I tune after building?
Yes. Build slightly long when possible. Then trim the driven element slowly while checking resonance and feed match.