The "DL special DX" for 15 meters band.

During the planning stage of the preparation for my 9L expedition, I was searching web pages looking for an antenna which:
- has some gain since I planned to use my IC 7000 without PA
- is easy to built and tune
- is not heavy - air baggage limitation
- preferably multiband

Among the others I noticed the "DL-special DX" . I have contacted Georges ON6WG/F5VIF designer of his antenna and after the exchange of a few e-mails, I built the 15 m band version with the horizontal line on the bottom (mechanically easier one since you need only 5m "boom"). I have tested this antenna for a short time at home, comparing it to my inverted "V". Since the results were positive, I built the version with the horizontal wire on top as recommended by the author of this antenna. This version was installed at Waldi SP7GXP mast 8 meters above the ground, tuned with MFJ-259, and then Waldi made tests of this version using his sophisticated antenna analyzing equipment AIM 4170C. The AIM 4170C antenna analyzer showed that this antenna in the point of its resonance and min SWR has the Impedance 50 Ohm and True Phase Angle almost "0" (no inductive or capacitive reactance present). It means no need for any matching system, and one can expect a high efficiency of this antenna. The practice on the air confirmed it. If only it could be a multiband antenna....
And here we are.

On the left there is scheme of the antenna I built. Given dimensions are the one after tuning to 21.050 MHz

For calculation of the length of the one loop I used the old formula:

300 / F MHz x 1.05 - results are in meters

You need two loops so the wire must be twice as long as the calculation is.
Keep the bottom part of the antenna at least a quarter wave above the ground!

Here you see the way I attached the wire.
The horizontal part is made with a stronger wire since it must support the fishing rod to avoid too big a sag of it. A wire is attached to the fishing rod with a strong tape of any type.
At the bottom apex, some 10 cm of wire is left for tuning the antenna to the frequency you wish.
My antenna was tuned to 21.050 ( SWR 1:1.15) since I preferred CW operations, but even though at the SSB end, SWR was 1:1.8.

This sketch shows some construction details.
Keep in mind that this antenna was made for temporary use during the expedition only, think, some reinforcements should be done for permanent use.
To the insulator plate (8 x 40 cm) is attached an aluminum "L" shape bar 0.5m long. The fishing rod (make sure it is not made of carbon) is attached to the "L" shape bar with plastics strips. The center of the coax cable is connected to the horizontal wire and the shield to the bottom wire.
I prefer feeding my antennas with the half-wave long coax or its multiplicity. The half-wave-long coax does not transform impedance so the radio sees the same impedance which is present at the feeding point of the antenna.
You may determine the length of your coax cable (it works for monoband antenna only) according to formula:
[(300/F) x n]/2 where: F - frequency in Megahertz, "n" means any number so that the coax reach your radio
For the physical length of the cable, we must multiply this result by the coax velocity factor VF eg. 0.66 for RG58.

Here is a photo of the center of the DL special DX just before going to the top of the mast.

I would like to underline that all credit is going to Georges ON6WG/F5VIF the designer of this antenna.

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