2m 3-Element Yagi — 144 MHz
3-element Yagi for 144 MHz. 4 mm parasitic elements, 6 mm driven element, 520 mm boom. Simulated in 4NEC2 at 1.5 m height, 11 segments per element.
Performance Data
| Gain | 7.17 dBi |
| F/B | 13.9 dB |
| -3 dB E-plane (vertical) | 116° |
| -3 dB H-plane (horizontal) | 78° |
| Impedance at 145 MHz | 48.87 + j0.02 Ω |
| SWR min | 1.01:1 @ 145 MHz |
| SWR bandwidth (< 1.5:1) | > 144–146 MHz (full band) |
| Refl. coeff. | −40.6 dB @ 145 MHz |
| Polarisation | Horizontal |
| Boom length | 520 mm |
| Electrical length | 0.25 λ |
Geometry
Parasitic elements Ø 4 mm, driven element Ø 6 mm — all insulated from boom. Positions from reflector end.
| Element | Position (mm) | Length (mm) | Ø (mm) |
|---|---|---|---|
| Reflector | 0 | 1014 | 4 mm |
| Driven | 317 | 1000 | 6 mm |
| Director | 520 | 914 | 4 mm |
More diameter columns will be added as they are simulated. Do not use these lengths with a different rod diameter without re-simulating.
Pattern & SWR Plots
Build Notes
Feed: Direct 50 Ω. Split driven element (6 mm) at centre with ~5 mm gap. Centre pin to one half, shield to the other.
Driven element: 6 mm aluminium rod (1000 mm). Parasitic elements are 4 mm rod.
Boom: Non-conductive (fibreglass, PVC, wood) = simplest. Metal boom = insulate elements. Through-boom on metal = re-simulate with boom correction.
Precision: At 144 MHz, 1 mm ≈ 0.15 MHz shift. More forgiving than UHF, but still measure carefully.
Cable: RG-213 or better. Cable loss at 144 MHz is moderate — keep runs reasonable.
Polarisation: Horizontal as built. Rotate boom 90° for vertical (FM).
Materials
| Item | Qty | Specification |
|---|---|---|
| Aluminium rod (4 mm) | ~2 m total | 6061-T6 or similar — reflector + director |
| Aluminium rod (6 mm) | ~1 m | 6061-T6 or similar — driven element |
| Boom | ~600 mm | 15–20 mm square or round (aluminium, fibreglass, PVC) |
| Insulated clamps | 3 | Nylon or HDPE, sized for 4 mm / 6 mm rod |
| SO-239 or BNC connector | 1 | Panel mount, 50 Ω |
| Coaxial cable | 5–10 m | RG-213 recommended (50 Ω) |
| Stainless steel hardware | 1 set | M3 screws, nuts, washers |