Moxon Antenna Calculator

Welcome to our Moxon Antenna Calculator, a crucial tool for amateur radio enthusiasts and antenna builders. The Moxon Rectangle is renowned for its compact size, excellent front-to-back ratio, and relatively wide bandwidth, making it a popular choice for various applications from portable operations to fixed station use. Use the calculator below to quickly determine the dimensions for your next Moxon build.

What is a Moxon Antenna?

The Moxon Rectangle, often simply called a Moxon, is a two-element wire beam antenna. It's essentially a compact, rectangular version of a two-element Yagi antenna. Designed by Les Moxon, G6XN, its unique folded-end geometry allows for a smaller footprint while still delivering impressive performance, especially a strong front-to-back ratio and good gain for its size.

Its design typically consists of a driven element and a reflector, both bent at 90-degree angles at their ends to face each other. This configuration creates a highly efficient radiator that minimizes side lobes and maximizes directivity in the forward direction.

Why Choose a Moxon?

There are several compelling reasons why amateur radio operators opt for a Moxon antenna:

• Compact Size: Significantly smaller than a full-sized Yagi for the same frequency, making it ideal for limited space or portable operations.
• Excellent Front-to-Back (F/B) Ratio: Moxons are known for their superb F/B ratio, meaning they effectively suppress signals from the rear, reducing interference and enhancing desired signal reception.
• Good Gain: While not as high-gain as a multi-element Yagi, a Moxon offers respectable gain (typically around 5-6 dBi) for a two-element antenna.
• Wide Bandwidth: Compared to many other compact antennas, the Moxon often exhibits a wider operational bandwidth with a low SWR.
• Simple Construction: With only two elements and a straightforward geometry, Moxons are relatively easy to build using common materials like wire, PVC, or fiberglass spreaders.
• Low Sidelobes: The design inherently reduces unwanted radiation to the sides, focusing power where you want it.

Moxon Antenna Design Principles

The Moxon's effectiveness stems from its unique geometry. The driven element and the reflector are parallel for most of their length, but their ends are bent inward, creating a capacitive coupling between the tips. This coupling is what makes the antenna electrically shorter and contributes to its excellent performance characteristics.

The six key dimensions (A, B, C, D, E, F) determined by our calculator define this specific rectangular shape. These dimensions are critical for achieving the desired resonance, impedance, and radiation pattern for a given operating frequency. While the formulas provide a solid starting point, minor adjustments during tuning are often necessary due to environmental factors, material choices, and construction tolerances.

Using the Moxon Antenna Calculator

Our calculator simplifies the process of designing your Moxon antenna. Here's how to use it:

1. Enter Operating Frequency: Input your desired operating frequency in Megahertz (MHz) into the provided field. For example, for the 20-meter amateur band, you might enter 14.200.
2. Select Output Units: Choose whether you want the dimensions displayed in Meters, Feet, or Inches.
3. Click "Calculate Dimensions": The calculator will instantly provide the six critical dimensions (A, B, C, D, E, F) based on established Moxon formulas.

Remember, these calculations are for the center frequency. For operation across an entire band, consider designing for the middle of your preferred segment.

Building Your Own Moxon Antenna

Constructing a Moxon antenna is a rewarding project for many radio amateurs. Here's a general overview of the steps involved:

Materials You'll Need:

• Wire: Copper or aluminum wire (e.g., #12 or #14 AWG) for the elements.
• Spreaders/Frame: Non-conductive materials like PVC pipe, fiberglass rods, or even bamboo for the frame to hold the elements in shape.
• Insulators: To isolate the elements from the frame and each other.
• Coaxial Cable: Typically 50-ohm coax (e.g., RG-8X, RG-213) for feeding the driven element.
• Balun (Optional but Recommended): A 1:1 current balun at the feed point helps prevent common mode current on the coax.
• Hardware: Clamps, bolts, UV-resistant zip ties, etc., for assembly.

Basic Construction Steps:

1. Cut Elements: Cut your wire elements to the calculated lengths (A, C, E, F). Remember to account for extra length for bends and connections.
2. Form the Rectangle: Create the rectangular shape using your spreaders and insulators. Ensure the elements are taut and maintain the calculated distances.
3. Feed Point: Connect your coaxial cable to the center of the driven element (dimension A). Pay attention to proper soldering and weatherproofing.
4. Mounting: Attach the completed Moxon to a mast or support structure.
5. Tuning: Use an antenna analyzer or SWR meter to fine-tune the antenna. Slight adjustments to element lengths or spacing may be needed to achieve the lowest SWR at your desired frequency.

Common Applications

The versatility of the Moxon antenna makes it suitable for a wide range of applications:

• Amateur Radio (HF, VHF, UHF): Popular for contesting, DXing (long-distance communication), and general rag-chewing due to its directional properties.
• Portable Operations / Field Day: Its lightweight and relatively easy-to-deploy nature make it excellent for temporary setups.
• Satellite Communication: For low-earth orbit (LEO) satellites, a Moxon can provide the necessary gain and directivity.
• Fixed Station Use: As a primary or secondary antenna, especially when space is a constraint for larger Yagis.

Advanced Considerations

• Element Diameter: The formulas used are typically for thin wire elements. Using very thick elements or tubing can slightly alter the electrical length, requiring minor adjustments.
• Height Above Ground: Like all antennas, the performance of a Moxon is affected by its height above ground. Generally, higher is better, but even at lower heights, a Moxon can outperform omnidirectional antennas.
• Environmental Factors: Proximity to metal objects, trees, or buildings can detune an antenna. Always tune the antenna in its final operating environment.
• Moxon Rectangle vs. Yagi: While related, the Moxon is not just a 'bent Yagi'. Its unique coupling provides different characteristics, often better F/B for its size, but generally less gain than a Yagi with the same number of elements.

Conclusion

The Moxon antenna offers an excellent balance of performance, size, and ease of construction, making it a fantastic choice for many amateur radio operators. Whether you're chasing DX on the HF bands, operating portable, or just looking for a compact directional antenna, the Moxon is a design worth considering. Use our calculator as your first step towards building a highly effective Moxon antenna and enjoy the world of directional communications!