6. 18 MHz
Delta Zepp Antenna

A mature technology
The Zepp/Zeppelin antenna has been around for more than 100 years.

The antenna presented here adopts the Zepp-feed and is currently in use at my station. It is an 18-MHz wire antenna.

Sure enough, the likes of "mono-band / wire" are out of fashion. But it will not be so bad to have a glimpse of such a "mature technology".

Delta-Zepp
The overall configuration is as in the illustration below.
The caption was tentatively chosen from its appearance.


The so-called Zepp employs a half-wave radiation element and a quarter-wave parallel-wire feeder. While mine has a full-wave radiator, and it is bent at the 3 points to form a triangle.

Although it is delta-shaped, the element tip is left open as in the above.


Thus, the current distribution on the radiator is, as in the right figure, minimum at the delta apex and base center, and maximum at both oblique sides, resulting in the vertical polarization.


The feed method is the same as that of Zepp, ie, to find out 50-ohm point slightly above the shorted lowest end for direct connection with a 50-ohm coax.

Further the feeder's lowest point is connected to a steel pipe of the antenna mast to prevent noises caused by static which occasionally appears on the antenna element.

The responses of DX stations and the received signals of IBP beacons all suggest a farily good performance of this antenna.
　
In addition, the interference to the audio systems in the shack is minimum compared with other antennas.

An unfortunate aspect is that its resonance point shifts significantly during the rainfall. Probably this is because, as often pointed out, the feed method itself, ie, feeding at the element-edge rather than at the center, is far from the ideal.

The right is a mesurement result for the freq - SWR response, at usual condition.


Still, I feel that nothing could replace this feature of the 50-ohm direct feed and the element direct-grounding. So I intend to continue using this antenna for some time.