Moxon Calculator
Professional Antenna Dimension Modeler
Total Width (Dimension A)
0.722 m
0.098 m
1.742 m
2.562 m
Formula based on standard Moxon coefficients: A=0.351λ, B=0.051λ, C=0.007λ, D=0.123λ, E=0.181λ
Antenna Geometry Visualization
Proportional sketch of your Moxon Rectangle layout.
What is a Moxon Calculator?
A moxon calculator is a specialized tool used by amateur radio operators and antenna engineers to determine the specific dimensions of a Moxon Rectangle antenna. Invented by Les Moxon (G6XN), this antenna is a folding of a two-element parasitic array, traditionally a driven element and a reflector. The moxon calculator simplifies the complex geometry of this “folded Yagi” to provide five critical dimensions that ensure the antenna resonates at the desired frequency while maintaining a high front-to-back ratio.
Who should use a moxon calculator? Anyone looking for a compact, directional antenna with a broad footprint. Unlike traditional Yagi antennas, the Moxon design uses folded ends to reduce the overall width by approximately 25%, making it ideal for small yards or portable operations. A common misconception is that the moxon calculator only works for wire antennas; in reality, it is equally effective for rigid tubing designs, provided the wire diameter is factored into the final tuning.
Moxon Calculator Formula and Mathematical Explanation
The math behind the moxon calculator relies on the wavelength (λ) of the target frequency. The primary challenge in Moxon design is the critical spacing of the “tips” of the driven element and the reflector. This gap creates capacitive loading that allows the antenna to be physically shorter than a standard dipole while maintaining a 50-ohm impedance.
| Variable | Meaning | Typical Coefficient (λ) | Unit |
|---|---|---|---|
| A | Overall Width | 0.351 | Meters/Feet |
| B | Driven Element Side Length | 0.051 | Meters/Feet |
| C | Gap Between Ends | 0.007 | Meters/Feet |
| D | Reflector Side Length | 0.123 | Meters/Feet |
| E | Total Depth (B+C+D) | 0.181 | Meters/Feet |
Step-by-step calculation using the moxon calculator logic:
1. Calculate Wavelength: λ = 299.79 / Frequency (MHz).
2. Multiply λ by the specific coefficients (A, B, C, D) to get raw lengths.
3. Adjust for wire diameter (thicker elements require slightly shorter physical lengths for the same electrical resonance).
Practical Examples
Example 1: 20-Meter Band (14.150 MHz)
When you input 14.150 MHz into the moxon calculator, the wavelength is approximately 21.18 meters. The calculator yields a width (A) of 7.43m and a total depth (E) of 3.83m. This antenna would provide a gain of roughly 6 dBi and an exceptional front-to-back ratio exceeding 25 dB, perfect for chasing DX with a small footprint.
Example 2: 6-Meter Band (50.125 MHz)
For VHF enthusiasts using a moxon calculator at 50.125 MHz, the dimensions shrink significantly. The width (A) becomes 2.10m, and the depth (E) is only 1.08m. Because of its small size, this version is often built using aluminum tubing, which provides excellent bandwidth and structural integrity.
How to Use This Moxon Calculator
Using our moxon calculator is straightforward and designed for immediate accuracy:
- Enter Frequency: Input your target center frequency in Megahertz (MHz).
- Specify Wire Diameter: Enter the thickness of your material. For wire, use the converted mm value (e.g., 14 AWG is 1.6mm).
- Select Units: Choose between Meters, Feet, or Inches based on your measuring tape.
- Analyze Dimensions: Review the A, B, C, D, and E values. Pay special attention to Dimension C (the gap), as this is the most critical for tuning.
- Review the Diagram: Use the generated SVG chart to visualize the assembly and ensure your wire bends are in the correct direction.
Key Factors That Affect Moxon Calculator Results
- Element Diameter: As the diameter of the wire or tube increases, the antenna’s bandwidth increases, but the required physical length decreases. The moxon calculator accounts for this “velocity factor” shift.
- Height Above Ground: Like all horizontal antennas, the Moxon’s impedance and take-off angle are affected by ground proximity. A moxon calculator provides “free space” dimensions which are best used at heights of 1/2 wavelength or more.
- Insulation: If using insulated wire, the velocity factor decreases, requiring you to shorten the elements by 2-5% compared to the moxon calculator output.
- Material Conductivity: Copper has higher conductivity than aluminum or stainless steel, affecting the efficiency and Q-factor of the design.
- Proximity to Objects: Metallic structures near the antenna will detune the moxon calculator results, necessitating field trimming.
- Feedpoint Matching: The Moxon is inherently close to 50 ohms, but slight variations in construction may require a 1:1 balun for optimal SWR.
Frequently Asked Questions (FAQ)
The Moxon often provides a better front-to-back ratio and a more convenient 50-ohm match than a standard closely-spaced 2-element Yagi, making the moxon calculator a preferred tool for many builders.
Yes. You can mount the Moxon rectangle vertically. This is popular for FM broadcast or local VHF/UHF communication.
Dimension C (the gap) is vital. If this gap is incorrect, the front-to-back ratio will degrade quickly. Always use a moxon calculator to double-check this spacing.
If built correctly using the moxon calculator, the SWR is typically below 1.5:1 across the entire band, removing the need for an external tuner.
While possible by nesting rectangles, it is complex. Most users calculate separate dimensions for each band using a moxon calculator.
Copper wire is standard. If using steel wire, the loss will be higher, though the moxon calculator dimensions remain similar.
Most builders use PVC or fiberglass spreaders to hold the shape defined by the moxon calculator.
Check for nearby metal objects or incorrect gap spacing (Dimension C). Re-run the moxon calculator to ensure your measurements were precise.
Related Tools and Internal Resources
- antenna gain calculator – Compare the dBi of your Moxon against other designs.
- yagi uda calculator – For those needing more gain than a 2-element array can provide.
- swr calculator – Measure the efficiency of your feedline and antenna match.
- dipole length calculator – The fundamental calculation for all wire antenna projects.
- ham radio tools – A complete suite for amateur radio hobbyists.
- rf propagation calculator – Predict how your Moxon signal will travel across the globe.