OK1M 7-element multiband Yagi for 20/15/10 m

A 7-element multiband antenna for contesting on the 20, 15 and 10 m bands: 2 elements on 20 m, 2 on 15 m and 3 on 10 m, all on a 4.36 m boom with a single 50 Ω feed line. It is a shorter sister of the 9-element version.

Design

Only the 20 m driven element is fed. It is split in the centre, and the 15 m and 10 m driven elements are continuous open-sleeve elements coupled from it. The antenna was modelled and optimized with OK1M-PyminiNEC3 for flat SWR across 14.000–14.350, 21.000–21.450 and 28.000–28.700 MHz.

Computed performance

Model v0.3, 12 m above real ground (ε = 13, σ = 5 mS/m):

Band	Elements	SWR	SWR < 2	Ga [dBi]	F/B [dB]	Elevation
20 m	2	1.03–1.34	whole band	11.2–11.7	9.8–13.3	23.7°
15 m	2	1.27–2.62	21.079–21.423	10.7–11.6	8.7–10.8	16.2°
10 m	3	1.04–2.15	28.042–28.683	12.3–12.6	13.4–16.5	12.2°

The upper part of the 10 m band is outside the optimized range – SWR reaches 6.8 at 29.0 MHz.

Elements

Element	From boom rear end [mm]	Length [mm]	Tubes [mm]
REF 20 m	30	10 974	30 / 25 / 20 / 16
REF 15 m	439	7 130	20 / 16
REF 10 m	1 482	5 100	16
DE 15 m	2 764	6 846	20 / 16
DE 20 m (feed)	3 030	10 294	30 / 25 / 20 / 16
DE 10 m	3 185	5 166	16
D1 10 m	4 330	4 788	16

Construction

• Boom – 35×35×2 mm, one piece 4 360 mm without joints, 3.1 kg
• Elements – telescopic aluminium tubes with a 150 mm overlap, tightened with hose clamps
• Insulators – polypropylene tube clamps on laser-cut aluminium plates
• Mast plate – at the centre of gravity, 1 900 mm from the rear end of the boom
• Feed – 1:1 current balun at the 20 m driven element
• Mass – approx. 15.9 kg without coax and balun

Documentation

The repository contains the MMANA-GAL models, the full bill of materials with a cutting plan, drilling drawings and DXF files of the plates.

• Repository: git.ok1kvk.cz/RybkaLabs/multiband-hf-antenna-7el-ok1m-20-15-10m
• Web documentation: ih9.ok1m.cz/antennas/ok1m-7el-multiband

Update: the antenna was used at 12 m at IH9/OK1M – see the report from CQ WW DX SSB 2026.

73 & TNX