MMANA-GAL Tutorial: Building Your First HF YagiThis tutorial walks you step-by-step through designing and modeling a basic HF Yagi antenna using MMANA-GAL. It assumes you are familiar with basic antenna terms (dipole, gain, feedpoint, SWR) but are new to MMANA-GAL. By the end you’ll have a working model, understand how to interpret results, and know how to iterate toward better performance.
About MMANA-GAL
MMANA-GAL is a free antenna modeling program based on the Method of Moments. It’s widely used by ham radio operators for quickly predicting antenna performance, including radiation patterns, gain, impedance, SWR, and element currents. While not as feature-rich as full commercial packages, MMANA-GAL is lightweight, fast, and very capable for common HF and VHF antenna types.
What you’ll build
We’ll model a simple 3-element Yagi for 20 meters (14.200 MHz) with a driven element, one reflector, and one director. Target goals:
- Resonant around 14.200 MHz
- Reasonable forward gain (~6–8 dBi)
- Acceptable feedpoint impedance near 50–75 Ω
- Front-to-back ratio suitable for general use
Step 1 — Install and launch MMANA-GAL
- Download MMANA-GAL from its official site or a trusted source and install it.
- Launch the program. You’ll see a grid and a set of input fields for element geometry, frequency, and other parameters.
Step 2 — Set basic parameters
- Open the “Antenna” / “Parameters” dialog (menu varies by version).
- Set Frequency to 14.200 MHz.
- Set Wire Diameter to something realistic (e.g., 2.5–4.0 mm for aluminum tubing; 1.8–2.0 mm for galvanized steel). This affects end effects and impedance.
- Set the ground type to “Free space” or “Real ground” depending on whether you plan to model ground effects. For initial design, free space is fine.
Step 3 — Define the elements
Yagi layout convention: elements are placed along the X-axis with the driven element at the origin or near it. MMANA-GAL uses node coordinates to define wires.
For a simple starting point, use these approximate lengths and spacings (initial guesses; we will tune them):
- Reflector (Element 1): Length = 10.90 m, Position X = -0.25 m (behind driven element)
- Driven element (Element 2): Length = 10.40 m, Position X = 0.00 m
- Director (Element 3): Length = 9.90 m, Position X = 0.45 m (in front of driven)
These are approximate for a 20 m Yagi; adjust after simulation.
To enter them:
- Use the “Wire” or “Element” editor.
- Create straight horizontal wires centered at their X positions. For each element, set Y = 0 for simplicity and Z = desired height above ground (e.g., 10 m). In free-space modeling, height matters only for ground-included runs.
Example coordinates for driven element (centered at origin, 10.40 m long, along Y-axis):
- Left end: (X=0.00, Y=-5.20, Z=10.0)
- Right end: (X=0.00, Y=+5.20, Z=10.0)
Repeat similarly for reflector and director with their lengths and X offsets.
Step 4 — Set feed and segmentation
- Assign the feed point to the center of the driven element. In MMANA-GAL, select the driven wire and specify the segment number corresponding to its center (MMANA often auto-segments; ensure the driven element has an odd number of segments to place the feed exactly at the center).
- Segmentation: A good rule is 10–20 segments per wavelength for accuracy, but MMANA-GAL often defaults to a reasonable value. For 14.2 MHz, wavelength λ ≈ 21.1 m, so aim for segment lengths < λ/10 (~2.1 m). Shorter segments near feed/ends improve accuracy.
Step 5 — Run the initial simulation
- Click “Execute” or “Calculate”.
- MMANA-GAL will show results: input impedance (R + jX), SWR curve, gain, radiation pattern, and element currents.
Key outputs to check:
- Feedpoint impedance (aim ~50 Ω real, low reactance).
- SWR at 14.200 MHz (preferably < 2:1).
- Gain (dBi).
- Front-to-back ratio (dB).
- Radiation pattern (azimuth and elevation plots).
Step 6 — Tuning the design
Common adjustments:
- If resonance is low (reactance inductive), shorten the driven element slightly. If capacitive, lengthen it. Adjust in small steps (1–3 cm) and re-run.
- Reflector: usually slightly longer than driven (increase length to move resonance lower). Move reflector further back to increase front-to-back but watch impedance changes.
- Director: shorter than driven; move closer or farther to tweak gain and impedance.
Example tuning steps:
- If impedance too high (>70 Ω), slightly lengthen driven or move director closer.
- If gain is low, adjust director spacing and length for better forward coupling.
- For higher F/B, increase reflector length or move it slightly further from the driven.
Iterate until feedpoint R ~50–75 Ω and SWR acceptable.
Step 7 — Add practical details
- Add a realistic feedline model (coax, with choke or balun) to see effects on SWR. MMANA-GAL can simulate coax feed sections and loss.
- Model the boom as a non-conductive or conductive member if it’s metal; that can affect resonant lengths slightly. Use thin wires positioned appropriately.
- Add mounting hardware, element end insulators, and support wires if they’re conductive and near the elements.
Step 8 — Analyze patterns and performance
- Inspect azimuth plot for beam width and peak gain.
- Check elevation plot for takeoff angle. For general DX on 20 m, you want a lower takeoff angle (5–15°) for long-distance propagation; adjust height above ground to lower the main lobe.
- Use the SWR vs frequency plot to estimate bandwidth. Yagis have limited bandwidth; thicker elements or parallel parasitic elements increase bandwidth.
Step 9 — Exporting and building
- Export the element lengths, coordinates, and segment data into a parts list. MMANA-GAL often provides element lengths directly.
- When building, cut elements slightly longer than modeled (accounting for end effects and fittings), then trim to tune on the actual tower using an antenna analyzer.
- Use good mechanical practices: proper guying, insulating mounts, and corrosion-resistant materials.
Quick example final dimensions (approximate)
- Reflector: 10.90 m
- Driven: 10.40 m
- Director: 9.90 m
- Spacing: Reflector to Driven 0.25 m; Driven to Director 0.45 m
- Boom length: at least distance from reflector to director plus mounting clearance
- Height above ground: 10 m (adjust for desired takeoff angle)
Troubleshooting tips
- Strange reactance swings: check segmentation and ensure no overlapping wires or duplicate nodes.
- Very low gain or multiple lobes: check element alignment and symmetry; ensure elements are colinear and horizontal.
- Feedpoint far from 50 Ω: experiment with director spacing and driven length; consider a matching network or balun.
Further learning
- Try 4- and 5-element Yagis for higher gain.
- Compare MMANA-GAL results with on-air SWR and field-strength measurements.
- Read community designs and optimization reports to learn element spacing trends.
This should get you from zero to a working MMANA-GAL model of a 3-element 20 m Yagi. If you want, I can provide a ready-to-import MMANA-GAL file (.maa format) with coordinates and segment values for these dimensions.
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