DL-Special DX simple but exceptionally powerful antenna

We talked about the DL-Special DX antenna once with Vilo, OM3CAQ. In amateur radio operation, we are constantly looking for solutions that offer a good compromise between performance, ease of construction and low costs. One such solution is an antenna DL-Special DX, ktorú navrhol a prakticky otestoval Georges ON6WG/F5VIF. Táto špeciálna konfigurácia dvoch fázovo spojených delta slučiek (collinear delta loops) ponúka Directional radiation, High profit a low beam angle, čím je ideálna pre DX prevádzku.

Origin of the antenna and first experiences

Koncept antény vznikol v roku 1992, keď sa ON6WG pripravoval na ťažký „pile-up ' from the anticipated FOØCI DXpedition from Clipperton Island. Without access to a profitable directional antenna, he decided to create an antenna that would be simple to manufacture, cheap and effective. He found inspiration in books Low Band DXing (ON4UN) a The Radio Amateur Antenna Handbook (W6SAI, W2LX). The result was an antenna that allowed him to connect with FOØCI on the third call without any problems, thus confirming its qualities.

DL-Special DX antenna concept

This antenna consists of two of triangular delta loops, ktoré sú zavesené špicom nadol (tvar dvojitého „V“). Sú umiestnené v the same vertical plane a phase connected in the upper corners, where the power coaxial cable is also connected. Thanks to this configuration, the antenna behaves like a phased array, which increases the gain and improves the directivity of the radiation.

It is a big advantage resonant resistance close to 50 ohms, čo znamená, že antenna does not need any tuning element (tuner). After correct setting, it is effective PSV very low (close to 1:1 ), which allows efficient operation without losses.

Calculation and construction

The total length of the conductor for one delta loop is determined according to the relationship:

• in feet: λ = 1005 / f(MHz)

• in meters: λ = 300 / f(MHz)

Subsequently, the conductor is cut to 1.06 λ, čo je optimálna dĺžka slučky pre rezonanciu. Pre dve slučky (DL Special DX) sa celková dĺžka vodiča zdvojnásobí. antenna sa môže zhotoviť ako simple wire construction with several insulators, mounted on a frame or between two masts.

On bands VHF or higher, the antenna can be placed on a frame (e.g. made of PVC) and even attached to a window or balcony. On the sq bands, even if it is only placed at a height of 1/4 λ, it offers a lot low beam angle, čo je ideálne pre spojenia na veľké vzdialenosti.

Power supply and balun

DL-Special DX is symmetrical antenna, a preto je vhodné použiť 1:1 balun (eg 'choke balun'). In practice, this means stringing several together ferrite toroids to the coaxial at the power point. This avoids the post-shielding current and maintains the symmetry of the radiation.

Radiant properties and gain

Modeling in the 4nec2 Software showed that the antenna has a 145 MHz band (VHF) placed at a height of 1/4 λ above the ideal ground surface:

• Gain up to 11 dBi, čo je porovnateľné so four-element yagi antenna

• Radiation angle is very low - ideal for DX operation

• Horizontal radiation diagram shows directivity with a wide main lobe

On the sq bands, the antenna has similar characteristics. In practice, this means that even in low height (e.g. 5-6 meters above the ground) quality connections can be established over thousands of kilometers.

Bandwidth and SWR

Both measurements and modeling confirm that the antenna has wide range of applicability with a very low PSV. On the 28 MHz band, it covers the entire band with minimal reflection, which allows use without the need for tuning.

Polarization

One of the advantages of DL-Special DX is Dual polarization – both horizontal and vertical. On sq bands it helps to reduce the influence QSB . On VHF, it allows simultaneous communication with both horizontally and vertically polarized stations without switching the antenna.

Comparative tests

The DL-Special DX was tested against a four-element yagi antenna on the 144 MHz band. In tests where both antennas were at the same height on separate masts, the quality of the received and transmitted signals was comparable. This is proof that this simple wire antenna can really match a more expensive directional solution.

Practical use – DXpedition 9L1BTB

An interesting application of the DL-Special DX is its use during a DXpedition SP5BTB as 9L1BTB in Sierra Leone in 2013. The antenna was made for the 15 meter band and placed on jediný stožiar. Fungovala výborne.

Advantages of DL-Special DX antenna and conclusion

DL-Special DX is a simple, cheap and light antenna suitable for DX operation. It is single band antenna, ale vďaka nízkej náročnosti na materiál si ju možno postaviť pre viacero pásiem. Niekoľko hlavných výhod:

• High profit

• Directional radiation with a low angle

• 50 ohm impedance – simple power supply

• Wide band with low PSV

• Dual polarization

• Simple assembly and disassembly

• Low price and easy availability of material

If you are looking for an original and efficient single-band solution - whether for home use, in the field or on a DXpedition - the DL-Special DX is an excellent candidate. With minimal effort and low costs, you will get an antenna with a performance that will surprise even the opposing stations.

Springs

[1] 9L1BTB – SIERRA LEONE 2013 DX-pedition

[2] https://on6wg-f5vif.online/Doc/DL-Special%20DX%20Antenna%20-%20Engl.pdf

[3] https://www.QRZ .com/db/S51X