Moxon Calculator
This powerful Moxon Calculator provides the exact dimensions needed to build a high-performance Moxon antenna for any frequency. Enter your target frequency and select your units to get started.
Enter the desired center frequency for your antenna in MHz.
Choose the measurement unit for the calculated dimensions.
Antenna Total Width (A)
Dimensions are based on industry-standard formulas developed by L.B. Cebik, W4RNL, for a 50-Ohm feedpoint impedance.
What is a Moxon Antenna? A Deep Dive into this Compact Beam
A Moxon antenna, often called a Moxon rectangle, is a two-element directional antenna known for its compact size and outstanding performance. Named after its inventor, Les Moxon (G6XN), this antenna is a type of parasitic array, similar to a Yagi, but with the element ends folded towards each other. This unique design results in an antenna that is approximately 70% the width of a full-size dipole, making it an excellent choice for amateurs with limited space. The two elements are the driven element (which is fed with the coaxial cable) and a slightly longer, passive reflector. This configuration produces a cardioid radiation pattern, which means it has strong signal strength in one direction (forward gain) and excellent rejection of signals from the rear (high front-to-back ratio). This makes the Moxon calculator an essential tool for designing an antenna that can reduce interference from unwanted directions. Another key advantage is its native 50-ohm feedpoint impedance, which means it provides a perfect match for standard coaxial cables without requiring complex matching networks.
Moxon Calculator Formula and Mathematical Explanation
The magic behind any Moxon calculator lies in a set of empirical formulas refined by L.B. Cebik (W4RNL). These formulas are derived from the fundamental relationship between an antenna’s size and the frequency it operates on, defined by the wavelength (λ).
The core steps are:
- Calculate Wavelength (λ): The wavelength is the starting point for all calculations. It’s found by dividing the speed of light (c) by the desired frequency (f). The formula is: λ = c / f.
- Calculate Dimensions: Each dimension of the Moxon antenna is a specific fraction of the calculated wavelength. These fractions have been optimized through extensive modeling to achieve the desired 50-ohm impedance and high front-to-back ratio.
This Moxon calculator uses the following standard constants:
- Dimension A (Total Width): A = 0.732 * (λ / 2)
- Dimension B (Driven Element Side): B = 0.129 * (λ / 2)
- Dimension C (Gap): C = 0.155 * (λ / 2)
- Dimension D (Reflector Side): D = 0.089 * (λ / 2)
- Dimension E (Total Driven Element Length): E = 2*B + C
- Dimension F (Total Reflector Length): F = 2*D + A
| Variable | Meaning | Unit | Typical Range |
|---|---|---|---|
| f | Frequency | MHz | 1.8 MHz – 440 MHz |
| λ | Wavelength | Meters | Depends on frequency |
| A | Total width of the antenna frame | m, cm, in, ft | ~37% of λ |
| B | Length of the driven element “tail” | m, cm, in, ft | ~6% of λ |
| C | Gap between element tails | m, cm, in, ft | ~7% of λ |
| D | Length of the reflector “tail” | m, cm, in, ft | ~9% of λ |
| E | Total length of driven element wire | m, cm, in, ft | A + 2*B |
For more advanced designs, check out our Dipole Antenna Calculator.
Practical Examples (Real-World Use Cases)
Let’s see how our Moxon calculator works with two common amateur radio scenarios.
Example 1: 20-Meter Band DX Chasing
An operator wants to build a Moxon for the popular 20-meter DX (long-distance) segment.
- Input Frequency: 14.200 MHz
The Moxon calculator provides the following dimensions (in meters):
- Dimension A (Width): 7.78 m
- Dimension B (Driven Tail): 0.69 m
- Dimension C (Gap): 0.82 m
- Dimension D (Reflector Tail): 1.56 m
- Driven Element (Total): 9.16 m
Interpretation: The operator can build a compact beam antenna with a width under 8 meters, which easily fits in a small backyard, while providing significant gain and interference rejection for contacting far-away stations.
Example 2: 6-Meter “Magic Band” Opening
Another operator wants a lightweight antenna for the 6-meter band, known for its unpredictable long-distance openings.
- Input Frequency: 50.125 MHz
The Moxon calculator yields much smaller dimensions:
- Dimension A (Width): 2.20 m
- Dimension B (Driven Tail): 0.19 m
- Dimension C (Gap): 0.23 m
- Dimension D (Reflector Tail): 0.44 m
- Driven Element (Total): 2.58 m
Interpretation: This antenna is small enough to be portable or mounted on a simple mast. It’s perfect for field day operations or for quickly setting up an effective antenna to take advantage of sporadic E-layer propagation. To explore other portable designs, consider a guide on building HF antennas.
How to Use This Moxon Calculator
Using this Moxon calculator is a straightforward process designed to get you from frequency to finished design in seconds.
- Enter Frequency: Input your desired operating frequency in MHz. This is the center of the frequency range you want your antenna to be most efficient at.
- Select Units: Choose your preferred unit of measurement from the dropdown menu (meters, feet, inches, etc.). The calculator will automatically convert all output dimensions.
- Review Primary Result: The main highlighted result is Dimension A, the total width of the antenna. This is often the most critical dimension for determining if the antenna will fit in your available space.
- Note Intermediate Values: The calculator provides all other key dimensions (B, C, D, and the total lengths E and F). These are the measurements you’ll use to cut your wires or tubing.
- Visualize with the Chart: The dynamic SVG chart provides a top-down view of your antenna. Use it to visualize how the dimensions relate to each other.
- Build and Tune: Cut your elements according to the calculated dimensions. While this Moxon calculator is highly accurate, it’s always a good practice to check the SWR (Standing Wave Ratio) with an analyzer and make minor adjustments to the element lengths for a perfect match. Learning about understanding SWR is crucial for this step.
Key Factors That Affect Moxon Calculator Results
While the Moxon calculator provides a very strong starting point, several real-world factors can influence the final performance of your antenna.
- Height Above Ground: This is one of the most significant factors. A Moxon’s radiation angle and feedpoint impedance change with its height above the ground. A height of at least a half-wavelength is often recommended for optimal performance.
- Wire Diameter/Tubing Size: The thickness of the material used for the elements affects the antenna’s bandwidth. Thicker elements generally provide broader SWR curves, meaning the antenna will perform well over a wider range of frequencies.
- Construction Materials: Whether you use copper wire, aluminum tubing, or another conductor will have a minor effect on the resonant frequency due to differences in conductivity and velocity factor.
- Nearby Objects: Metal objects like gutters, wiring, and other antennas can interact with the Moxon’s electromagnetic field, detuning it and altering its radiation pattern. Ensure the antenna is placed as far from other conductors as possible.
- Feedpoint Construction: How you connect your coaxial cable to the driven element is important. A well-sealed, robust connection will prevent impedance bumps and ensure long-term reliability. A 1:1 balun or choke is often recommended to prevent feedline radiation. Compare this to the feed on a Yagi-Uda Antenna vs Moxon.
- Accuracy of Cuts: While the design can be forgiving, strive for accuracy when cutting your elements. Being precise to within a small percentage of the calculated lengths will get you very close to the target frequency without needing major adjustments.
Frequently Asked Questions (FAQ)
1. What is the main advantage of a Moxon antenna?
The primary advantages are its compact size (about 70% of a full-size dipole) and its excellent front-to-back ratio, which provides great rejection of interfering signals from behind the antenna. The direct 50-ohm feed is also a major convenience.
2. What is a typical gain of a Moxon antenna?
A typical Moxon antenna provides around 2.0 dBi of forward gain. While a 2-element Yagi might have slightly more gain, the Moxon’s superior front-to-back ratio is often more desirable in crowded band conditions.
3. How critical is the gap (Dimension C) in the Moxon calculator?
The gap dimension is quite important for achieving the best front-to-back ratio and the 50-ohm impedance match. While small deviations won’t cause total failure, it’s one of the dimensions to pay close attention to during construction.
4. Can I build a Moxon with wire instead of tubing?
Absolutely. Moxon antennas are very commonly built using wire stretched on a non-conductive frame (like fiberglass poles or PVC). This construction method makes for a very lightweight and portable antenna. Using a Moxon calculator is the first step for either method.
5. Is a Moxon better than a dipole?
A Moxon is a directional antenna, while a standard dipole is omnidirectional (in the horizontal plane). If you want to focus your signal in a specific direction and reduce interference from other directions, the Moxon is far superior. If you need to communicate in all directions equally, a dipole is a better choice. See our Dipole Antenna Calculator for comparison.
6. Do I need an antenna tuner with a Moxon?
If built correctly according to the Moxon calculator dimensions, you should not need an antenna tuner. The design is intended to provide a near-perfect 50-ohm match at the design frequency. A tuner might be helpful if you want to operate far from the center frequency. Explore more on our page about antenna tuners explained.
7. How do I feed a Moxon antenna?
You feed a Moxon at the center of the driven element (the shorter of the two main elements). The coax center conductor connects to one side of the gap, and the shield connects to the other side. A 1:1 current balun is recommended at the feedpoint.
8. Can I mount a Moxon antenna vertically?
Yes. Mounting a Moxon vertically will result in vertically polarized signals. This is common for local FM repeater access on VHF/UHF bands. For long-distance HF communication, horizontal polarization is almost always used.