moxon calculator

What Is a Moxon Antenna?

A Moxon rectangle is a compact, two-element directional antenna based on a folded-and-bent Yagi-style geometry. It uses a driven element and a reflector, with the element ends turned inward. This geometry reduces overall size while maintaining useful forward gain and excellent front-to-back rejection.

Radio operators love the Moxon for VHF, UHF, and HF portable work because it is:

• Smaller than many equivalent 2-element Yagi designs
• Simple to build with wire and a lightweight spreader frame
• Effective for reducing unwanted signals from the rear
• Friendly to portable, field-day, and backpack installations

How This Moxon Calculator Works

This calculator uses wavelength-based proportions to generate a practical first-cut set of Moxon dimensions. You provide frequency, conductor diameter, and velocity factor. It then estimates key geometry values such as:

• Overall width and height of the rectangle
• Total driven-element and reflector wire lengths
• Element-to-element spacing
• Tip gap and feed gap starting dimensions

Core Equation

The base wavelength relationship used is: wavelength (meters) = 300 / frequency in MHz. From this, the calculator applies typical Moxon proportions and light corrections for conductor size and velocity factor.

Why Real-World Tuning Still Matters

Antennas interact with nearby structures, support materials, height above ground, and coax routing. That means no formula can perfectly predict final resonance in every setup. Treat calculated results as a smart baseline, then trim and adjust while measuring SWR or impedance.

Input Guide

Design Frequency (MHz)

Use the center frequency where you want the best match and pattern. For example, if you operate across 2 meters, you might target 146 MHz as a balanced midpoint.

Conductor Diameter (mm)

Thicker elements usually broaden bandwidth and slightly alter resonant length. Enter the actual diameter of your wire, rod, or tubing conductor.

Velocity Factor

For bare wire, values near 0.98 to 1.00 are common assumptions in practical calculators. Insulated wire may shift effective electrical length. If unsure, start at 0.98 and tune in small increments.

Build Notes for Better Results

• Keep both elements symmetric left-to-right for predictable pattern performance.
• Use non-conductive spreaders (fiberglass, PVC, wood) to preserve calculated geometry.
• Route feedline away from the feedpoint at a right angle for a short distance before dropping down.
• Add a current choke (1:1 balun) at feedpoint to reduce common-mode current on coax shield.
• Measure twice before cutting; trim only a little at a time during tuning.

Typical Tuning Workflow

• Cut elements to calculator dimensions.
• Assemble frame and verify all gaps and spacing are accurate.
• Mount antenna clear of metal objects and test at intended operating height if possible.
• Check SWR/resonance with an analyzer.
• If resonance is low in frequency, shorten driven element slightly.
• If resonance is high, lengthen driven element or increase effective length using small pigtails.
• Re-check front-to-back performance after major geometry changes.

What Performance to Expect

A well-built Moxon commonly provides useful forward gain over a dipole and strong suppression of signals from behind. Exact numbers vary by frequency, height, ground conditions, and construction tolerance, but many builders target practical gain in the roughly 5 to 6 dBi class and front-to-back values that are noticeably better than simple omnidirectional antennas.

Final Thoughts

If you want a directional antenna that is compact, inexpensive, and effective, the Moxon rectangle is a great project. Use the calculator above as your starting point, then fine-tune in the real environment where you will operate. That combination—good math plus measured adjustments—is where excellent antenna performance comes from.