Two-element quad at 144 MHz

Quads prevail over other types of directional antennas on 2m VHF pomerne ťažko. Dôvod? Oveľa väčší odpor vetru, ktorý kladú oproti klasickým yagi antennas, which places much greater demands on the mechanical construction of the antennas, mast and rotator. Two-element quad je koncipovaný ako fixná anténa na domácom QTH, napríklad na prevádzače či paket. Záleží však len na šikovnosti konštruktéra, či ju dokáže urobiť prenosnú. Výroba jednoduchej verzie však nie je náročná a používa len dostupný materiál.

In addition to a decent gain, the advantage of the quad is that it is a 100% walkable antenna, which outperforms Slim-jims, collinear and similar antennas. In my experience it also outperforms the HB9CV which is an excellent antenna. Quad has the advantage of being directly fed by a coaxial cable (50 and 75 ohm) without any adjustment circuit and a smaller number of variables forming the antenna (circuit R and Ž and their mutual spacing). Adjustments - if necessary - are made PSV metrom na minimálne PSV. Podľa polohy napájacieho bodu môžeme zvoliť vertikálnu alebo horizontálnu polarizáciu.

The drawing shows a classic quad design of a two-element quad for horizontal polarization. Vertical is achieved by turning it 90 degrees so that the power supply is on the left or right. Both the boom and spacers must be made of non-conductive material, and the part of the mast extending into the antenna area should also be made of non-conductive material.

The most ideal is the attic hanging version fixedly turned in the desired direction. We can only do with a supporting structure made of wood, or from wood and PVC. The solution is best captured in photographs. However, it must be said that there are no limits to experimentation, in the ARRL Antena Book there is also a 2-el.quad in a folding design (like an umbrella).

Quad antenna dimensions

• emitter circumference: 206 cm (side 51.75 cm and distance at power terminals 1 cm)
• reflector circumference: 216 cm
• spacing Ž – R: 0.15 to 0.25 lambda according to the required impedance at the supply point. For a 50 ohm power supply, the optimal distance between the elements is about 35 cm
• element material diameter: 6 mm

Attunement

2-el.quad is a relatively wide-band antenna and therefore it is sufficient to fine-tune it by changing the element spacing to at least PSV. We connect to the antenna via PSV meter radio station and measure PSV. Increasing the spacing increases the impedance, decreasing it decreases. The profit changes only minimally.