The DK7ZB-5-Band-Quad The DK7ZB-3-Band-Quad The Oblong The Extended Oblong

The Oblong for the Shortwave Bands

The Picture 1 left shows the classic Quad-Element. The circumference is about 1 lambda, the side-lengths are 0,25 λ. For horizontal polarisation the Quad is fed in the part 1 or 3. The currents show maxima in this two parts. For the impedance and the radiation patterns the two different Quads (Quad-shape and Diamond-shape) show the same data!

The gain is 1,1-1,2 dBd and the feedpoint impedance 130 +/- j 0 Ω .

The Quad is a stacked system, but for higher gain the two stacked parts 1 and 3 are to close together.

But how we can increase the gain? Let as take a look on Picture 2 ! The distance between 3 and 4 increased from 0,25 to 0,4 λ. By comparing the patterns we see where the gain of 2,6 dBd is coming from.

The data of Oblongs with different lengths for the vertical and horizontal parts:

Circumference

Hor.

Vert.

Impedance

Gain

1,13  λ

0,186 λ

0,378 λ

50  Ω

2,29 dBd

1,12 λ

0,153 λ

0,406  λ

33 Ω

2,62 dBd

1,11 λ

0,136 λ

0,420  λ

25  Ω

2,77 dBd

 

 

 

The Oblong for 14 MHz with a feedpoint impedance

 of 48 Ω and a gain of 2,5 dBd

The Aluminium tube must be interrupted in the middle part for the feeding. With a wire for part 5 the losses are greater. As monoband antenna you can feed this with a quarterwave-coax-choke. Better is the feeding with a twin-wire as Wireman-cable and an antenna tuner.

The antenna can be used for the 17-m-Band as an extended Oblong with very good DX-results, 30 m is possible, too.

As supporting structure you can use a flag pole or a glass fibre mast, but a metal support is possible. Mount the antenna as high as possible for a low vertical radiation angle.

For other bands use the data in the table above.