Build a 2-Element Yagi Antenna
The 2-element Yagi is the most accessible entry point into directional HF antenna building — two parallel aluminum elements on a single boom, producing genuine forward gain and front-to-back rejection from a structure that fits on a modest rotatable mast. A 20m 2-element Yagi spanning 33 feet delivers 3–5 dBd of forward gain over a dipole and 10–15 dB of front-to-back rejection, all for a materials cost under $150 and a few weekend hours of construction. This guide covers element sizing, boom construction, element-to-boom mounting, the gamma match feed system, and the tuning procedure for a 20m 2-element Yagi suitable for tower or mast mounting.
Driven Element and Reflector
The 2-element Yagi uses one driven element (connected to the feedline) and one parasitic reflector (not connected to the feedline) spaced behind the driven element. The reflector is longer than the driven element and its spacing is chosen so that the re-radiated signal from the reflector adds constructively in the forward direction and destructively behind:
Spacing vs Performance Trade-offs
The element spacing is the primary design variable in a 2-element Yagi. Different spacings optimise different performance parameters:
Feedpoint Impedance and Matching
The mutual coupling between the driven element and reflector lowers the driven element feedpoint impedance below the 73 Ω of a standalone dipole. At 0.2λ spacing, the feedpoint is approximately 25–35 Ω — requiring a matching network to connect to 50 Ω coax:
2-Element Yagi vs Other Antennas
Understanding where the 2-element Yagi fits in the antenna landscape helps set realistic expectations:
- vs dipole at same height: 3–5 dBd forward gain (equivalent to 2–3× transmitter power) plus directivity that reduces QRM from unwanted directions. The Yagi is unambiguously better for DX from the same tower height.
- vs 3-element Yagi: the 3-element adds approximately 2 dBd more gain and 5–10 dB more front-to-back rejection. If tower space and boom length allow, the 3-element is worth the extra effort. The 2-element is the right choice when boom length must be kept under 15 feet or when the build is a first foray into Yagi construction.
- vs vertical at ground level: at the same tower height, the Yagi's horizontal polarisation has a higher radiation angle than a vertical — the Yagi is better for medium-distance DX; the vertical is better for the very lowest elevation angles needed for very long-distance paths. In practice, a 20m Yagi at 40+ feet outperforms a ground-mounted vertical for most DX contacts.
- vs commercial 2-element Yagi: a homebrew 2-element Yagi using the dimensions in this guide matches the performance of commercial antennas costing $300–600. The construction quality of the element-to-boom connections and the matching network implementation are the variables that determine whether the homebrew version matches or exceeds commercial performance.
| Band | Frequency | Driven element | Reflector | Spacing (0.2λ) | Boom length |
|---|---|---|---|---|---|
| 10m | 28.400 MHz | 16.5 ft (5.03 m) | 17.3 ft (5.27 m) | 6.9 ft (2.10 m) | 6.9 ft |
| 12m | 24.940 MHz | 18.8 ft (5.73 m) | 19.7 ft (6.00 m) | 7.9 ft (2.41 m) | 7.9 ft |
| 15m | 21.200 MHz | 22.1 ft (6.73 m) | 23.2 ft (7.07 m) | 9.3 ft (2.83 m) | 9.3 ft |
| 17m | 18.100 MHz | 25.9 ft (7.88 m) | 27.2 ft (8.27 m) | 10.9 ft (3.32 m) | 10.9 ft |
| 20m | 14.150 MHz | 33.1 ft (10.09 m) | 34.7 ft (10.58 m) | 13.9 ft (4.24 m) | 13.9 ft |
| 40m | 7.150 MHz | 65.5 ft (19.96 m) | 68.8 ft (20.97 m) | 27.5 ft (8.38 m) | 27.5 ft |
Yagi 2 Element Calculator
This design has published dimensions for more than one band. The default shown below is the first/most common one on the page -- change the frequency and recalculate for the other bands.
Materials for a 20m 2-element Yagi with gamma match, covering 14.0–14.35 MHz
How the Gamma Match Works
The gamma match is the most practical feed system for a homebrew 2-element Yagi. It connects a 50 Ω coax to the lower-impedance Yagi feedpoint without requiring a split driven element or a balun, and it is adjustable after installation:
Gamma Match Component Dimensions
Starting dimensions for the gamma match on a 20m 2-element Yagi with 0.2λ spacing. These are starting points — final adjustment is done with the NanoVNA after installation:
Building the 20m 2-Element Yagi
This guide builds a 20m 2-element Yagi with tapered aluminum element sections and a gamma match feed. Build and verify the boom and element assemblies on the ground before mounting at height. The gamma match is tuned with the antenna at its final installed height.
Cut the Boom
Cut the 2-inch OD aluminum tubing to 14 feet for the boom. Deburr both ends. Drill a 1/4-inch hole through the boom at each element position — these holes accept the U-bolt hardware for element mounting. The two hole positions are:
Build the Driven Element
The driven element is a split dipole — the two halves are electrically isolated from each other at the center (where the gamma match and feedpoint connect). Each half telescopes from a 1.25-inch center section to 1.0-inch outer sections:
Build the Reflector Element
The reflector is a continuous element — it does not need a center gap and can contact the boom directly. Construction mirrors the driven element but with the reflector length (34.7 ft total, 17.35 ft per half at start):
Mount Elements to Boom
Mount both elements to the boom on the ground before raising. The element U-bolt saddle assemblies clamp the element center section to the boom top surface. For the driven element, the HDPE insulator plate sits between the element saddle and the boom. For the reflector, the saddle sits directly on the boom.
Orient both elements in the same plane — both horizontal, both pointing in the same directions (for example, both pointing North-South if the boom runs East-West). Verify alignment by sighting along the boom: the elements should form a perfect cross with the boom, not twisted or tilted. Any twist in the element plane distorts the radiation pattern.
Build and Install the Gamma Match
The gamma match mounts at the driven element center, parallel to one half of the driven element. Construct it before raising the antenna:
- Cut the 3/8-inch gamma rod to 24 inches as a starting length
- Fabricate two small standoff brackets from aluminum angle stock or purchased antenna bracket hardware — these hold the gamma rod parallel to the driven element at 5 inches spacing. Mount one bracket at the driven element center (at the feedpoint gap) and one bracket 24 inches along the element half.
- Install the series variable capacitor in-line with the gamma rod, at the feedpoint end. The capacitor connects between the coax center conductor and the gamma rod. House the capacitor in a small weatherproof box mounted at the feedpoint.
- Connect the coax shield to the driven element center (at the boom crossing point). Connect the coax center conductor to the inner end of the gamma capacitor. The outer end of the gamma capacitor connects to the gamma rod.
- Install the current choke (FT-240-31, 5–6 turns of coax) immediately below the feedpoint where the coax departs down the mast.
Verify Balance Point and Mount to Mast Bracket
Before raising, verify the antenna's mechanical balance point — the point along the boom where the antenna balances horizontally. This is where the mast mounting bracket attaches. Support the completed antenna at various boom positions until it balances level; mark this point.
Raise and Pre-Tune Elements on the Ground
Before raising to final height, lay the antenna horizontally at ground level and connect the NanoVNA to verify basic operation. Sweep 13.5–15 MHz and look for a dipole-like resonance near 14.150 MHz. The resonance will not be at exactly the target frequency — the presence of the reflector shifts the driven element resonance. This is normal and expected. Look for a resonance dip anywhere in the 13–15 MHz range that responds to changing the gamma capacitor setting.
Raise to Operating Height and Tune
Raise the antenna to its operating height. Connect the NanoVNA at the shack end of the coax. Sweep 13.5–15.5 MHz. The antenna should show a clear SWR minimum somewhere in or near the 20m band. Tune the gamma match to center the resonance at 14.150 MHz and bring SWR below 1.5:1:
Trim Element Lengths and Verify Final Performance
Once the gamma match is optimised and resonance is near 14.150 MHz, verify the reflector is contributing correctly to the pattern by checking front-to-back ratio on-air. Point the antenna at a known station and note the S-meter reading, then rotate 180° and note the reading again. A well-built 2-element Yagi should show a 10–15 dB (2–3 S-unit) front-to-back difference.
Document: driven element final length, reflector final length, gamma capacitor setting (turns of rotation from minimum), SWR at resonance, SWR at band edges, front-to-back measurement, and antenna height. Photograph the feedpoint assembly and gamma match. Apply self-amalgamating tape and RTV sealant to weatherproof the feedpoint enclosure, all coax connections, and the gamma capacitor housing.
| Symptom | Most likely cause | Diagnosis | Fix |
|---|---|---|---|
| No SWR dip visible in 13–15 MHz sweep | Driven element shorted to boom or open circuit in gamma match | Check DC resistance from coax center to shield at shack — should be open circuit | Verify HDPE insulators between driven element and boom; check gamma capacitor connections |
| SWR minimum present but cannot get below 2:1 with gamma adjustment | Gamma rod length incorrect for the feedpoint impedance | Try lengthening gamma rod to 30 inches — if SWR improves, rod was too short | Adjust gamma rod length in 2-inch increments; re-optimize capacitor after each change |
| SWR minimum at correct frequency but pattern has no front-to-back | Antenna pointing backward — reflector is in front | Check boom orientation — driven element must be at the FRONT (toward target) | Rotate antenna 180° on mast; driven element must point toward the target direction |
| Resonance drifts with temperature — shifts 50+ kHz from morning to afternoon | Loose element joint or corroded joint changing length with temperature | Identify drifting joint by flexing each section — corroded Noalox joint may have higher resistance too | Tighten all hose clamps; re-apply Noalox; install lock bolt through each joint overlap |
| RF in shack — SWR varies with coax routing | No current choke — coax shield radiating and forming part of antenna | Reposition coax at feedpoint — if SWR changes, coax is carrying common-mode current | Install FT-240-31 current choke immediately below the feedpoint |
| Front-to-back ratio below 8 dB | Reflector length incorrect or element spacing error | Measure reflector length — should be 5% longer than driven element at resonance | Adjust reflector to correct length; verify element spacing is within 6 inches of 13.9 ft |
Does a 2-element Yagi need a balun?
The gamma match is inherently unbalanced — one side of the driven element connects to the coax shield and the other to the gamma rod and coax center. This means the driven element is already fed asymmetrically, and a conventional balun is not appropriate at the feedpoint. What is needed is a current choke (also called a common-mode choke) immediately below the feedpoint on the coax — this prevents the coax shield from carrying RF current back toward the shack, which would distort the pattern and cause RF in the shack. An FT-240-31 toroid with 5–6 turns of coax, or a W2DU-style choke (ferrite beads on the coax), provides excellent common-mode suppression without affecting the wanted differential-mode signal.
Can I build a 2-element Yagi for 40m?
Yes — the same design scales directly to 40m. The boom length grows to 27.5 feet, the driven element to 65.5 feet, and the reflector to 68.8 feet. A 40m 2-element Yagi requires a substantial tower (typically 60+ feet for DX performance) and a heavy-duty rotator due to the wind loading of the long elements. The mechanical engineering becomes the primary challenge at 40m — each element is nearly 70 feet long and requires a tapered tube design with multiple section changes to keep the element from sagging. Many operators building 40m Yagis use truss wires supporting the element tips to prevent droop. The electrical design is identical to the 20m version; the mechanical design is significantly more demanding.
How much gain does a 2-element Yagi actually produce in real-world operation?
In practice, the 3–5 dBd gain is real and operationally significant. A 2-element 20m Yagi at 40 feet consistently outperforms a dipole at the same height for DX contacts — the gain advantage is equivalent to increasing transmitter power from 100W to 200–300W, and the directivity reduces QRM from unwanted directions during pile-up operation. However, the gain is not as dramatic as the numbers suggest to newcomers: 3 dBd = half an S-unit stronger signal at the other end. The directivity advantage is often more practically valuable than the gain advantage — being able to null out a strong interfering station by rotating the beam is a qualitative operating improvement that cannot be achieved with any omnidirectional antenna.
What height is required for a 20m 2-element Yagi to be effective?
Any height is better than none, but the practical minimum for DX operation is approximately 30 feet (roughly λ/2 at 20m). At 30 feet the Yagi's primary radiation lobe is at approximately 30° elevation — useful for medium-distance DX but not optimal for the very low-angle propagation paths needed for extreme DX. At 50–60 feet (λ or greater), the lobe drops to 20° or below — the sweet spot for consistent worldwide DX on 20m. Many operators mount a 2-element Yagi at 30–40 feet on a simple push-up mast and find it an enormous improvement over a fixed dipole, even if not perfectly optimised for low-angle DX.
Is the gamma match the best feed system for this antenna?
The gamma match is the most practical for a homebrew build because it requires no modification to the driven element and is fully adjustable after installation. Its disadvantages are that it is asymmetric (can cause some pattern asymmetry if not carefully built) and requires the variable capacitor to be weatherproofed at height. The beta match (hairpin) is arguably cleaner — it uses a shorted stub and a split driven element, producing a balanced feed with no moving parts. The folded dipole driven element is the simplest of all — the 4:1 impedance transformation of a folded dipole brings the feedpoint impedance up to approximately 100 Ω at 0.2λ spacing, which a 2:1 balun matches to 50 Ω perfectly and repeatably without adjustment. For a first homebrew Yagi, the gamma match's adjustability makes it the better learning experience; for a permanent installation, the beta match or folded dipole approach is worth considering.
Can I use the same boom and mast hardware for a future upgrade to 3 elements?
Yes — this is an excellent long-term planning strategy. Size the mast and rotator for the 3-element Yagi from the start. A 3-element 20m Yagi has a boom of approximately 22–24 feet and weighs roughly 25–30 lbs with hardware — a thrust bearing rated for 50+ lbs and a rotator rated for 15+ sq ft wind loading handles either antenna. The 2-inch boom specified in this guide also suits a 3-element Yagi if extended to 24 feet. When the upgrade time comes, the existing boom can be extended with a sleeve coupler and a new director element added at the front. The driven element and reflector positions remain unchanged — only the director is new.