Moxon Antenna Calculator
Design and build a high-performance, compact Moxon beam antenna.
Antenna Design Parameters
Enter the target center frequency for your antenna (e.g., 14.2 for the 20m band).
Select the unit for the calculated dimensions.
Dynamic Chart & Data Table
Chart showing how key dimensions change across a frequency range.
| Frequency (MHz) | Dim A | Dim B | Dim C | Dim D | Dim E |
|---|
Table of calculated dimensions for various frequencies around your target.
What is a Moxon Antenna Calculator?
A moxon antenna calculator is a specialized tool used by amateur radio operators, RF engineers, and electronics hobbyists to determine the precise dimensions needed to construct a Moxon antenna. This type of antenna, named after Les Moxon (G6XN), is a compact 2-element directional beam antenna known for its excellent performance characteristics, including a high front-to-back ratio and a 50-ohm feedpoint impedance, which allows for a direct connection to standard coaxial cable without a complex matching network.
Unlike a standard Yagi-Uda antenna, the Moxon antenna’s elements are bent towards each other, creating a rectangular shape. This design significantly reduces the physical size (by about 30%) compared to a full-sized dipole or Yagi for the same frequency, making it an ideal choice for operators with limited space. The primary purpose of a moxon antenna calculator is to simplify the complex calculations required to achieve this optimal design, ensuring the antenna performs efficiently at the desired frequency.
Who Should Use This Calculator?
This tool is invaluable for anyone looking to build a directional antenna for HF, VHF, or UHF bands. Whether you are a licensed ham radio operator participating in “Field Day,” a DX-chaser seeking to improve your signal, or a hobbyist experimenting with antenna design, this moxon antenna calculator provides the accuracy needed for a successful build.
Common Misconceptions
A common misconception is that the smaller size of the Moxon antenna leads to a significant loss in performance. While there is a very slight reduction in forward gain compared to a full-sized 2-element Yagi, the Moxon’s exceptionally high front-to-back ratio often makes it a superior choice for rejecting interference from unwanted directions. This excellent directional quality is one of the main reasons people use a moxon antenna calculator for their projects.
Moxon Antenna Calculator Formula and Mathematical Explanation
The design of a Moxon antenna is based on formulas derived from extensive modeling and empirical testing, most notably by L.B. Cebik, W4RNL. The calculations are all relative to the wavelength (λ) of the target operating frequency.
The first step for any moxon antenna calculator is to determine the wavelength:
Wavelength (λ) in meters = 299.792 / Frequency in MHz
Once the wavelength is known, a set of specific coefficients are used to calculate the physical dimensions of the antenna’s driven element and reflector. These dimensions are universally labeled A, B, C, D, and E.
- Dimension A (Total Width): This is the length of the main driven element and reflector wires.
- Dimension B (Driven Element Tail): The length of the bent ends of the driven element.
- Dimension C (Gap): The critical spacing between the ends of the driven element and the reflector.
- Dimension D (Reflector Tail): The length of the bent ends of the reflector element.
- Dimension E (Total Depth): The total front-to-back spacing of the antenna (B + C + D).
| Variable | Meaning | Formula (based on λ in meters) | Typical Range |
|---|---|---|---|
| A | Driven Element / Reflector Length | A = 0.732 * λ |
~73% of wavelength |
| B | Driven Element End Length | B = 0.129 * λ |
~13% of wavelength |
| C | Gap Between Elements | C = 0.010 * λ |
~1% of wavelength |
| D | Reflector End Length | D = 0.153 * λ |
~15% of wavelength |
| E | Total Antenna Depth | E = B + C + D |
~29% of wavelength |
This table outlines the core mathematical relationships used by the moxon antenna calculator.
Practical Examples (Real-World Use Cases)
Using a moxon antenna calculator is best understood through practical examples for popular amateur radio bands.
Example 1: 20-Meter Band (DX Chasing)
An operator wants to build a Moxon for the popular DX frequency of 14.200 MHz.
- Input: Frequency = 14.200 MHz
- Calculator Process: The moxon antenna calculator first finds λ = 299.792 / 14.200 ≈ 21.11 meters. It then applies the coefficients.
- Outputs (approximate):
- Dimension A: 15.45 meters (50.7 ft)
- Dimension B: 2.72 meters (8.9 ft)
- Dimension C: 0.21 meters (0.7 ft)
- Dimension D: 3.23 meters (10.6 ft)
- Dimension E: 6.16 meters (20.2 ft)
- Interpretation: The operator now has the exact measurements to build a highly effective, compact beam for making long-distance (DX) contacts on the 20-meter band. The total width is just over 15 meters, significantly smaller than a full-size dipole of over 21 meters.
Example 2: 6-Meter Band (VHF “Magic Band”)
An operator wants to explore the 6-meter band, targeting a frequency of 50.125 MHz (the DX calling frequency).
- Input: Frequency = 50.125 MHz
- Calculator Process: The moxon antenna calculator computes λ = 299.792 / 50.125 ≈ 5.98 meters.
- Outputs (approximate):
- Dimension A: 4.38 meters (14.37 ft)
- Dimension B: 0.77 meters (2.53 ft)
- Dimension C: 0.06 meters (0.20 ft)
- Dimension D: 0.92 meters (3.02 ft)
- Dimension E: 1.75 meters (5.74 ft)
- Interpretation: These dimensions result in a very manageable VHF antenna, small enough to be mounted on a simple rotator on a roof or mast. Its directional properties would provide significant advantages for weak-signal work on the “Magic Band.” Using a {related_keywords} could further optimize the setup.
How to Use This Moxon Antenna Calculator
Our moxon antenna calculator is designed for simplicity and accuracy. Follow these steps to get your custom antenna dimensions:
- Enter the Frequency: Input your desired center frequency in MegaHertz (MHz) into the primary input field. For example, for the 40-meter band, you might enter `7.15`.
- Select Your Units: Choose your preferred measurement unit from the dropdown menu (e.g., millimeters, inches, feet). The results will automatically convert.
- Review the Results: The calculator instantly provides the five critical dimensions (A, B, C, D, E). The “Primary Result” highlights the antenna’s total width (Dimension A), which is often the most critical factor for space considerations.
- Analyze the Chart and Table: The dynamic chart and data table show how the dimensions change for frequencies slightly above and below your target. This is useful for understanding the antenna’s performance across an entire band. This is a key feature of a good moxon antenna calculator.
- Build Your Antenna: Use the calculated dimensions to cut your wire or tubing elements. Remember that Dimension A is the full length of the straight wire sections, while B and D are the “tails” that are bent at 90 degrees. The gap, C, is the crucial space between the wire ends. It might be helpful to consult a {related_keywords} for construction tips.
Key Factors That Affect Moxon Antenna Results
While a moxon antenna calculator provides the ideal dimensions in a perfect world, several real-world factors can influence your antenna’s final performance.
- Wire Diameter/Tubing Size: Thicker elements will slightly shorten the required resonant length and increase the antenna’s SWR bandwidth. Our calculator uses formulas optimized for typical wire gauges, but very thick tubing may require slight adjustments.
- Wire Insulation: The plastic or rubber coating on a wire has a velocity factor that electrically “lengthens” the wire. If using insulated wire, you may need to shorten the elements by 2-4% from the calculated values. Always check SWR and trim as needed.
- Height Above Ground: This is one of the most critical factors. A directional antenna’s performance, especially its angle of radiation, is heavily dependent on its height in terms of wavelength. For long-distance HF contacts, a height of at least 1/2 wavelength is recommended. A lower height will result in a higher angle of radiation, which is better for local contacts.
- Construction Materials: The type of spreaders (fiberglass, PVC, bamboo) and insulators used can affect the antenna. Ensure insulators are of high quality, especially for high-power operation, and that spreaders are non-conductive. This ensures the moxon antenna calculator dimensions remain accurate.
- Nearby Objects: Metal objects like gutters, towers, and other antennas can interact with the Moxon’s electromagnetic field, detuning it and skewing its radiation pattern. Try to mount the antenna as far away from other conductive objects as possible. A {related_keywords} might help in analyzing these interactions.
- Feedpoint and Balun: A Moxon antenna has a balanced feedpoint. To connect it to unbalanced coaxial cable, a 1:1 balun (or choke balun) is highly recommended. This prevents the coax shield from radiating, which can distort the pattern and increase noise pickup.
Frequently Asked Questions (FAQ)
The excellent front-to-back ratio is achieved by carefully phasing the relationship between the driven element and the reflector. The specific spacing and element lengths, as determined by the moxon antenna calculator, create a deep null in the pattern to the rear of the antenna.
When built to the dimensions from a quality moxon antenna calculator, the feedpoint impedance is very close to 50 ohms. This results in a Standing Wave Ratio (SWR) of 1.5:1 or less across a useful portion of the band, often eliminating the need for an antenna tuner.
Yes, it’s possible to nest multiple Moxon antennas on the same set of spreaders for different bands. However, the design is complex as the elements will interact. This advanced project goes beyond the scope of a simple moxon antenna calculator and typically requires specialized modeling software.
Wire is lighter, cheaper, and easier to work with, making it ideal for portable or temporary setups. Tubing (usually aluminum) is more rigid, durable, and offers slightly wider bandwidth, making it better for permanent installations. Our moxon antenna calculator is suitable for both.
For horizontal polarization (most common for HF DX), the elements must be parallel to the ground. For vertical polarization (common for local VHF/UHF FM work), the elements must be perpendicular to the ground. You may want to use a {related_keywords} to decide which is best for your use case.
A Moxon antenna is essentially a quad loop with the top and bottom wires removed and the element ends bent. Its performance is very similar to a 2-element cubical quad, offering comparable gain and front-to-back ratio but in a mechanically simpler and often smaller package. The moxon antenna calculator simplifies one of the most popular modern antenna designs.
The gap is a critical dimension. If it’s too wide or too narrow, it will detune the antenna, affecting both the feedpoint impedance (SWR) and the front-to-back ratio. It’s important to follow the value from the moxon antenna calculator as closely as possible. Comparing with a {related_keywords} can be beneficial.
No, the Moxon is designed for a center feed. Feeding it off-center will unbalance the antenna, ruin the radiation pattern, and cause the SWR to rise dramatically. Always connect your feedline at the center of the driven element. Using a reliable {related_keywords} is key to success.