3.
14/18/21 MHz vertical antenna

Pictures at left and right sides are the antenna for 14/18/21 MHz.

The antenna is designed for 8-m long 18 MHz dipole, which bottom 2-m section is folded back to the upside. It is fed at this folded back point.

The original idea of this antenna came from a book, Ham Journal Series Nr. 9 / Manufacturing notes of fishing rod antennae / by JH1GNU, Kobayasi H. OM, published in H13 (2001). Here the author elaborates on the advantages of non-grounding antennas in a convincing manner.

Though the description is for 21 MHz, I made a 18 MHz version. As the tuning of this sort of off-center feeding looked awkward, I just let the automatic antenna tuner, AH-4, carry out this task without trying baluns or the likes.

It worked perfectly well and tuned smoothly not only to the 18 MHz, but also to the other 3.5/7/10/14/21 MHz bands!!

The illsutration below shows this design concept.



As this indicates, the current loop is at the position 1/8 λ apart from the feed point, in addition, the current at the feed point seen from the outside is zero because of the element folding. Thus the design seems to greatly reduce the various problems relating to the inteference with the objects at the immediate vicinity of the feed point such as buildings.

DX contacts on 14, 18 and 21 MHz bands improved markedly. TKS Kobayashi OM