Moxon Calculator
This powerful moxon calculator is a specialized tool for amateur radio enthusiasts to design and build a Moxon antenna. A Moxon antenna is a compact, 2-element beam with excellent front-to-back performance. Input your desired frequency to get the precise dimensions for your build.
Formula based on the widely used empirical formulas developed by L. B. Cebik, W4RNL. Dimensions calculated for wire antennas.
Dimensions Table & Visual Chart
| Dimension | Description | Meters (m) | Feet (ft) | Inches (in) |
|---|
Table showing all calculated dimensions for the moxon calculator in various units.
A dynamic visual representation of the Moxon antenna dimensions generated by the moxon calculator. The blue rectangle represents the driven element and the gray rectangle represents the reflector.
What is a Moxon Antenna?
A Moxon antenna, named after Les Moxon (G6XN), is a two-element rectangular antenna that is compact and highly efficient. It is essentially a modified Yagi antenna where the element ends are folded towards each other, which significantly reduces its physical size—about 30% smaller than a full-size 2-element beam. It should not be confused with a standard dipole or a simple loop antenna; its design is specifically engineered to create a directional radiation pattern. This makes the moxon calculator an essential first step for anyone wanting to build one.
This type of antenna is primarily used by amateur radio operators (hams) for HF (High Frequency) and VHF (Very High Frequency) communications. Its key advantages are a high front-to-back ratio, meaning it strongly rejects signals from the rear, and a direct 50-ohm feedpoint impedance, which allows it to be connected directly to standard coaxial cable without a complex matching network. A common misconception is that its small size compromises performance, but a well-built Moxon offers gain comparable to a 2-element Yagi.
Moxon Calculator Formula and Mathematical Explanation
The dimensions of a Moxon antenna are critical for its performance. The moxon calculator above uses a set of empirical formulas derived from extensive computer modeling by L.B. Cebik, W4RNL. These formulas calculate the lengths of the five key dimensions based on the desired frequency.
The calculation steps are as follows:
- Select Frequency (f): The operator chooses the center frequency in MHz.
- Calculate Wavelength (λ): Although not directly used in these simplified formulas, the dimensions are a fraction of the operating wavelength.
- Apply Constants: The calculator applies specific numerical constants to the frequency to find each dimension.
The core formulas used are:
- Dimension A (Driven Element Length) = 142.65 / f (MHz)
- Dimension B (Driven Element Tail) = 25.76 / f (MHz)
- Dimension C (Gap between Elements) = 4.27 / f (MHz)
- Dimension D (Reflector Tail) = 52.88 / f (MHz)
- Dimension E (Total Width) = B + C + D
| Variable | Meaning | Unit | Typical Range |
|---|---|---|---|
| f | Design Frequency | MHz | 3.5 – 144 MHz |
| A | Length of the main driven element | Meters | Varies with frequency |
| B | Length of the driven element “tail” or side | Meters | Varies with frequency |
| C | Gap between the driven element and reflector tails | Meters | Varies with frequency |
| D | Length of the reflector element “tail” or side | Meters | Varies with frequency |
| E | Total width of the antenna (Reflector side-to-side) | Meters | Varies with frequency |
Practical Examples (Real-World Use Cases)
Using a moxon calculator is the best way to get started. Here are two examples for popular amateur radio bands.
Example 1: 20-Meter Band (DX Chasing)
- Input Frequency: 14.200 MHz
- Calculator Outputs:
- Dimension A: 10.05 m
- Dimension E: 5.84 m
- Interpretation: An operator wanting to make contacts over long distances (DX) on the 20-meter band would build an antenna to these dimensions. The total length would be just over 10 meters, and the width just under 6 meters. This is significantly more compact than a traditional Yagi for the same band. For another great HF antenna option, check out our antenna design tool.
Example 2: 6-Meter Band (“The Magic Band”)
- Input Frequency: 50.125 MHz (SSB calling frequency)
- Calculator Outputs:
- Dimension A: 2.85 m
- Dimension E: 1.65 m
- Interpretation: For VHF enthusiasts, a 6-meter Moxon is very manageable. At under 3 meters long, it can be mounted on a simple rotator on a roof or mast. This setup is perfect for taking advantage of sporadic E-layer propagation for exciting long-distance contacts on a band known for its unpredictable openings. For a project like this, it’s a good idea to start with a reliable DIY antenna project guide.
How to Use This Moxon Calculator
- Enter Frequency: Type your desired operating frequency in MHz into the input field. The moxon calculator works in real-time.
- Review Primary Result: The large-font result ‘A’ is the most critical dimension—the length of the main radiating wire.
- Note Intermediate Values: The values for B, C, D, and E are the other key construction dimensions. Use the table to see them in meters, feet, and inches.
- Check the Chart: The SVG chart provides a visual scale of how the parts fit together, helping you avoid construction errors.
- Build and Tune: Cut your wires or tubes to these dimensions. While this moxon calculator provides very accurate starting points, minor adjustments may be needed to achieve a perfect SWR. Understanding the theory behind it can help; see our guide on understanding SWR.
Key Factors That Affect Moxon Antenna Results
Beyond the raw numbers from a moxon calculator, several real-world factors influence performance:
- Height Above Ground: This is one of the most critical factors. A higher antenna generally has a lower angle of radiation, which is better for long-distance communication (DX).
- Wire Diameter: Thicker wire can slightly increase the antenna’s bandwidth. The formulas used in this calculator are optimized for typical wire gauges (12-18 AWG).
- Construction Materials: Whether you use copper wire, aluminum tubing, or another conductor will affect the antenna’s longevity and performance. Insulated wire requires slightly different lengths than bare wire.
- Proximity to Objects: Keep the antenna as far away as possible from trees, buildings, and power lines. These objects can detune the antenna and block its signal.
- Feedpoint Construction: A weatherproof, well-constructed feedpoint is essential for long-term reliability. Using a balun (choke) is recommended to prevent feedline radiation.
- Accuracy of Dimensions: While forgiving, try to be as accurate as possible, especially with the gap (Dimension C), as it heavily influences the front-to-back ratio. Our HF antenna calculator guide provides more tips.
Frequently Asked Questions (FAQ)
1. Is a Moxon better than a Yagi?
A Moxon offers a much better front-to-back ratio and is more compact than a 2-element Yagi. However, a Yagi with 3 or more elements will have higher forward gain. The choice depends on your space and goals. Many start with a moxon calculator due to its simplicity.
2. Can I use this moxon calculator for any frequency?
Yes, the formulas are valid across the HF and VHF spectrum. However, for very high frequencies (e.g., above 150 MHz), the dimensions become very small and construction tolerances are tighter.
3. Do I need an antenna tuner with a Moxon?
If built correctly using a moxon calculator, the antenna should provide a 50-ohm impedance and a low SWR across a portion of the band, often eliminating the need for a tuner.
4. How do I feed a Moxon antenna?
You feed it directly in the center of the driven element (Element A) with 50-ohm coaxial cable. No special matching is required.
5. What is the gain of a Moxon antenna?
It typically provides about 2 dBd of forward gain, similar to a 2-element Yagi. Its main advantage is its high front-to-back ratio (often exceeding 20 dB).
6. Can I build a multi-band Moxon?
While some complex designs exist, the Moxon is inherently a single-band antenna. Trying to make it work on multiple bands compromises its performance significantly. For multi-band options, a different ham radio calculator might be more appropriate.
7. Does the orientation (horizontal vs. vertical) matter?
Yes. A horizontally mounted Moxon will have horizontal polarization, which is standard for long-distance SSB on HF. A vertically mounted one will have vertical polarization, common for FM operations on VHF.
8. What’s the best way to model a Moxon before building?
Advanced users can use software like EZNEC or 4nec2 to model the antenna’s performance. The dimensions from this moxon calculator provide an excellent starting point for such models. For more on this, see resources on portable beam antenna modeling.
Related Tools and Internal Resources
If you found this moxon calculator useful, you might also be interested in our other tools and guides for radio enthusiasts:
- Dipole Calculator: Calculate the length of a simple half-wave dipole antenna.
- Understanding SWR: An in-depth guide to Standing Wave Ratio and why it matters.
- Building a 20m Moxon Project: A step-by-step photo guide to building a wire Moxon.
- Yagi Antenna Calculator: Design multi-element Yagi antennas for higher gain.
- Choosing Your First HF Antenna: A beginner’s guide to the pros and cons of different antenna types.
- Guide to Antenna Modeling Software: An introduction to using software to predict antenna performance.