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Vertical Antenna Why a vertical antenna ? The specifications : - Must be efficient during DX operation - Must be inconspicuous (small, thin...). YL has always been very cooperative with my passion, however, rising a 120 ft tower in the backyard is an other story... - considering the backyard size, 1square meter sounds to be the maximum surface allowed, - the antenna has to have a very low wind surface. So, only a vertical antenna is able to answer the specifications, its very low radiation angle is very useful for DX and its low surface makes it ideal in case of strong wind etc... I-The antenna
This antenna is made from surplus military stuff. The base is made with a MP48 support (well known in the French police) and of 8 elements MS screwed one eachother which form the radiator element. Over 6 meters long, the radial is not self supporting and usually, the upper end succeeds to touch the ground very quickly. As the size of the antenna is 8 meters long a light set of guys is used to maintain it vertically. The set of guys is made with 2mm diameter nylon rope used by fishermen. The wind resistance is held very low and this antenna has been able to survive despite very strong tempest during the two last winters.
The MP48 stand is fasten on a base designed by Marcel F1UGH. This base is fasten itself to a concrete solid block (80X40X10 cm) with 4 screwed rods of 8mm in diameter. The overall assembly is very stable and more than sufficient to hold the antenna and the antenna coupler. II-Ground plane Vertical antennas are usually like quarter wavelenght (Marconi). They need a good ground plane or a counterpoise system to work correctly. We choose the ground plane. Knowing the poor quality of the ground, a set of galvanized water pipe has been buried in the ground. All the pipes are electrically connected together and to a 2 meter ground rod. The buried pipe are forming the letter "U" in the ground. The total length of the three branches of the "U"is a little bit more than 20 meters/
The SGC automatic antenna tuner "smartuner SG231" is used to feed the antenna at its lower part SGC. We had already used this antenna coupler during 3years (1998-2000) to match a 2X20m multiband dipole fed with a 300 ohms twin lead, a 1:4 unbalanced/balanced balun was used between the unbalanced output of the coupler and the line, to keep the symmetry of the antenna. This coupler was really well adpated to this job : all the 9 HF bands have been tuned without problem. Knowing in this case ,the coupler is part of the antenna, we tried to tuned the vertical rod using the SG231. After two years of operation, we could say that the result was far beyond our expectations. IV-Antenna schematic
This kind of configuration offers a complete system which uses on each band all the complete lenght of the antenna. It is consequently more efficient than the classic "trap vertical antenna". The commercial Butternut (HF-6V...) and Cushcraft (R7, R8...) which do not require an antenna coupler have the same philosophy however. Within two years, the antenna has proven it was particularly efficient during Dx operation (178 confirmed) despite the low RF power used (5W or less).
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