SQ5CBAFilip

Home  /  News  /  SQ4MN antenna for 2 m and 70 cm

News · 11 September 2026

An antenna you won’t find in any book

Marian assembled an antenna for two bands at once, 2 m and 70 cm, from elements left over after building two earlier antennas. Between the aluminium elements gleams a copper folded dipole, his own design. He won’t disclose the parameters: if he published them, they’d be taken as cheating, he says.

Marian SQ4MN — portrait
Marian SQ4MNdesign and photo · Warsaw
2 m + 70 cm copper folded dipole aluminium elements original design
Technical curiosities Share
Marian SQ4MN’s dual-band directional antenna on a balcony: a horizontal aluminium boom with vertical elements, two long and several short, and between them a tall, narrow dipole loop of copper tube; in the background a housing estate, a church and the skyscrapers of central Warsaw
11.09.2026 · SQ4MN’s balcony · photo: Marian
2bands in one antenna:
144–146 and 430–440 MHz
Cufolded dipole
from copper tubing
Althe other elements,
salvaged from two antennas
0published parameters
(on purpose)
Where it came from

From what was left over from two antennas

Anyone who builds antennas knows that drawer: rods, clamps and bits of tube that “will definitely come in handy one day”. For Marian they really did.

A third antenna from leftovers

Marian SQ4MN built two antennas, one for 2 m and one for 70 cm. There were elements left over. Instead of waiting for “someday”, they went onto a common boom and became an antenna that works on both bands at once.

The photo shows two families of aluminium elements: two long ones and a few clearly shorter. The elements stand vertically, so the antenna works in vertical polarisation, the same used by repeaters and FM contacts. Between them, instead of an ordinary rod, stands a tall, narrow loop of copper tube, curved in an arc at the top and bottom. In the background, above the treetops, the skyscrapers of central Warsaw.

“An antenna for two bands. Made from elements left over after building 2 m and 70 cm antennas. Works perfectly.”— Marian SQ4MN
Boom close-up: a copper folded dipole made of two parallel tubes, clamped to a plate on the aluminium boom; alongside, vertical aluminium elements and a cable run along the boom The heart of the antenna · dipole close-up
The most interesting element

Folded dipole from copper tubing

The builder has no doubt what the star is here. Let’s give him the floor.

“The most interesting element is the folded dipole made from copper tubing. It is my completely original solution, which I use in other antennas. I don’t like open dipoles.”— Marian SQ4MN

A plain open dipole is two rods with a gap in the middle to which the cable is connected. A folded dipole (also called a loop dipole in the literature, in English folded dipole) looks as if you put two dipoles in parallel and joined them at the ends into a narrow loop. The cable goes to the gap in only one leg; the other runs continuously. To the eye the difference is small; electrically it’s huge.

Open dipole: two vertical rods with a gap in the middle where the cable connects; current largest at the feedpoint, zero at the ends OPEN DIPOLE feedpoint current ≈ 73 Ω Folded dipole: a narrow loop of two parallel legs joined by arcs at the ends; the cable goes to the gap in one leg, the same current flows in both legs FOLDED DIPOLE feedpoint leg continuous ≈ 290 Ω · ×4

pulsing envelope = current distribution: greatest at the feedpoint, zero at the ends

× 4

Four times the impedance

The same current flows in both legs, so for the same power the feedpoint current is halved. Result: the impedance rises fourfold, in theory from about 73 Ω for a plain dipole to about 290 Ω.

290 Ω → 50–75 Ω

Made for a Yagi

The parasitic elements of a Yagi — the reflector and directors — lower the impedance of the driven element. A plain dipole can then drop clearly below 50 Ω, while a folded one ends up around 50–75 Ω. That’s why it so often feeds Yagi antennas, from TV to amateur radio.

wider bandwidth

Less fussy

A folded dipole has a wider operating bandwidth than a plain one: SWR rises more slowly as you move away from the centre frequency. In an antenna that has to cover a whole band — and here even two — that’s a very valuable trait.

Technical curiosities

A bit of physics around the copper loop

Marian won’t reveal how he designed his antenna, and we won’t guess. But antenna physics has a few lovely facts that show why copper, tubing and two bands make such an interesting combination.

skin effect 5 µm

Current flows on the surface

Radio‑frequency current hardly penetrates into the conductor. At 145 MHz it flows in copper mainly in a layer about 5 micrometres thick, and at 435 MHz about 3 µm, many times thinner than a human hair. The inside of a rod hardly conducts, so a tube performs like a solid rod, while being lighter and cheaper.

copper versus aluminium ≈ 1.6×

Copper conducts, solders and bends

Copper conducts about 1.6 times better than pure aluminium. Aluminium almost instantly covers itself with a hard oxide and without special fluxes you won’t solder it, which is why its joints are screwed and crimped. Copper solders without a fuss and is easy to shape, for example into the rounded loop ends you see in Marian’s dipole.

harmonics 3 × 145 = 435

Two metres related to seventy centimetres

A half‑wave dipole resonates not only at its own frequency but also at its odd multiples. You can see it clearly on HF: a 7 MHz dipole works as a 3/2 λ dipole at 21 MHz. The element then carries not half a wavelength but three half‑wavelengths.

And now the maths: 3 × 145 MHz = 435 MHz, the centre of the 70 cm band (430–440 MHz). The 2 m and 70 cm bands are related, which makes life much easier for dual‑band antenna designers. How Marian exploited that relationship is his secret.

The same element at two frequencies: at 145 MHz it is half a wavelength long and the current has one lobe; at 435 MHz it is three half‑wavelengths long and the current has three lobes, the middle one in antiphase 145 MHz · ½ λ + one current lobe · fundamental resonance 435 MHz · 3/2 λ + − + three lobes · 3 × 145 = 435 MHz
wavelength 103 cm · 34 cm

Two scales on one boom

Half a wave at 145 MHz is about 103 cm, at 435 MHz about 34 cm, one third as long. Yagi elements are about half a wavelength long, which is why a dual‑band antenna has “long” and “short” elements side by side. You can calculate the dipole dimensions for any band in the wire antenna calculator.

dBi − dBd 2.15 dB

Why numbers raise suspicion

Antenna gain is quoted relative to a dipole (dBd) or to an isotropic radiator (dBi), and the difference is 2.15 dB. Just leave the letter off and the antenna looks better than it is. No wonder results that are “too good to be true” arouse suspicion. Marian prefers his antenna to prove itself on the air, not in a table.

From Hertz to the balcony

A short history of Yagi antennas

Marian’s antenna is part of a family that turns exactly one hundred this year. Its history even includes a wartime anecdote.

1887

Heinrich Hertz and the first dipole

The German physicist is the first to demonstrate the existence of radio waves. He uses a setup we’d now call a dipole.

1926

Uda and Yagi, Tohoku University

Shintaro Uda develops a directional antenna with parasitic elements. His supervisor, Hidetsugu Yagi, describes it in English in 1928, which is why we commonly say “Yagi”, while the full name is Yagi-Uda.

1942

A surname that Japanese intelligence didn’t recognise

After taking Singapore, the Japanese seize a British radar technician’s notes about a “Yagi antenna”. The intelligence officers don’t recognise it as a Japanese surname. Only when the technician is interrogated does he explain that the antenna was named after a Japanese professor.

2026

SQ4MN, a balcony in Warsaw

From the parts of two antennas comes a third, for 2 m and 70 cm, with a copper folded dipole. You won’t find it in any book because, as the designer says, it came from his head.

Specifications

The designer’s secret

Instead of simulator plots there’s a single sentence: it works perfectly. The rest stays in the designer’s head.

“I don’t publish the specs because it would be taken as cheating on my part. You won’t find it anywhere in the literature, because it came from my head.”— Marian SQ4MN

A line like that works better than many a table: it makes you want to check straight away how this antenna performs. In amateur radio, an antenna is best judged by QSOs and reports, not catalogue numbers.

Want to know how it performs? Call SQ4MN on 2 m or 70 cm and ask for a report. And leave any questions for the designer in the guestbook.

Ask a question in the guestbook
Designer’s
secret

Antenna card

SQ4MN · 2 m / 70 cm · one-off
Bands
2 m and 70 cm
Dipole
folded, made from copper tube
Other elements
aluminium
Gain
dBd
SWR on 2 m
SWR on 70 cm
Front-to-back ratio
dB
Design source
SQ4MN’s head
Works
“perfectly” (according to the designer)
Marian SQ4MN — portrait SQ4MN
Author of the antenna and the photo

Marian SQ4MN

A radio amateur from Warsaw who designs antennas in his head and puts them up on his balcony. Earlier we showed his 70 cm Yagi with a second support under the boom, now a dual-band antenna with a copper folded dipole — a solution he also uses in other designs. We meet on the air and in person, for instance on 12 August on Most Świętokrzyski.

2 m + 70 cmhomebrewWarsawtext: Filip SQ5CBA
Read more

More of Marian’s antennas and more besides

The previous SQ4MN build, a survey of base antennas for 2 m and 70 cm, and a calculator to work out a dipole for any band.

SQ4MN 70 cm Yagi 2 m/70 cm base antennas Build your own Yagi Calculate a dipole