The “double” extended zeppelin antenna is made out of 2 X 5/8 wavelengths of wire and fed in the middle by a matching line to provide a 50 Ohms impedance.
The totale length of the antenna is roughly 13..14 meters.
The antenna can be placed in a horizontal or vertical configuration, and will exhibit a horizontal or vertical polarisation. It is not recommended to place it in an inverted V configuration.
The antenna not difficult to construct and is ideal for portable operation,but can also be welcomed to a base set-up. Infact it is my favourite vertical antenna, with its almost 5dBi freespace gain it beats any commercial availible vertical antenna.
Not bad for a piece of wire !
Below you will find a the first impression of how the antenna looks:
Above the horizontal freespace azimuth plot.
(click to enlarge)
Above the elevation plot when placed horizontal at 5,5 meters height above average ground.
(click to enlarge)
Above the elevation plot when placed horizontal at 11 meters height.
(click to enlarge)
Above the elevation plot when placed horizontal at 16,5 meters height above average ground.
(click to enlarge)
lets place the antenna vertical !
Above: When placed VERTICAL 3 meters from average ground conditions.
(tip height is 16,54 meters, click to enlarge).
In a vertical configuration the antenna is omni-directional.
(click to enlarge)
Above the SWR plot.
(click to enlarge)
For: 11 meter and 10m band
Antenna Type: Double extended Zeppelin
Designed by: 19DX348 version 1.01 march 2006
Gain: 4,94 dBI (@27,555 MHz)
Impedance: 50 ohms, direct fed
SWR below 1:1.1 > 150 Khz.
SWR below 2:1 > 850 Khz
Dimensions:
The antenna is made from 2mm diameter bare copper wire.
Wire nr 1 (at the bottom is the feedpoint) and is seperated 5cm.
Just connect the core of the coax to one leg and the braid to the other.
As alsways a 1;1 balun is adviced !
The wires 4 and 5 are 1,800 meters long
The wires 2 and 3 are 6,690 meters long
The gap between 4 and 5 is 16 centimeter.
That means the total antenna lenght is : 6,69+6,69 +0,16 = 13,54 meters.
SWR ADJUSTMENTS:
For initial testing, it is wise to leave wire 2 and 3 about 10cm longer.
You can change the SWR by folding back the ends of the two legs (2,3).
And just wrap it together with a tyrep.
If you make the antenna shorter the resonant point will be higher in frequency.
Lots of fun with litlle money spend !