Introduction
In the sixties two American amateurs have developed a theory using 4 phased verticals as a feasible alternative for low band directional antennas since the Yagis, due to their huge dimensions, bring intricate structural and mechanical problems which do require a large budget besides the engineering. This model did appear in March 1965 QST under the title "A Switchable Four Element 80-Meter Phased Array", by Dana Atchley, W1HKK/W1CF. Its exceptional performance as well as affordable cost made this configuration popular among the low band devoted followers, being used even in some DX-peditions as the 9M0C 1998 operation from th Spratly Island.
The Concept
Assuming that one side of the square is paralleled to the equator line the diagonals are pointing to Europe, Africa, Oceania and USA. The towers are fed with equal currents, so, when the European tower is switched on it will be being fed at -90 degrees, the side towers, e.g. the Africa and USA towers will be being fed at zero degree, while the Oceania tower will be being fed at +90 degrees. The signal direction will be toward the diagonal from the back to the front tower, it means, from +90 to -90 degrees, in this case the maximum gain will be toward the Europe. Obviously using a relay box the signal can be easily switched to anyone of the square vertices doing a roughly directional antenna. The -3 dB irradiation lobe is around 60 degrees and the take off angle is close to 17 degree.
There are 3 factors that directly do contribute to a vertical antenna performance:
The antenna simulation results showed the following:
These values are quite significant for a low band antenna. To learn more about the Pseudo-Brewester angle, please refer to the Low Band DXing book by John Delvodere published by the ARRL.
Dimensions
Construction
The towers were carefully designed to achieve the following goals:
Performance
At the very first measurement the antenna did show absurd SWR values in the NW to SW direction. A careful inspection in the whole system pointed out to an un-plugged connector in the phase box, that once fixed showed SWR following values:
3.500 | 3.650 | 3.800 | |
1:1,7 | 1:1,2 | 1:1,6 |
Please click here for the measurement complete report.
Conclusion
The pleasure to attend the 80 meters band without those so peculiar horrible crashes and clunks does worth all the planning, construction and time expended on it.
Credits
- Structural analysis: Eng Arthur Jose Magalhaes de Assis Bastos
- Foundation: Eng Cesar Augusto de Camargo Rodrigues
- Civil Works: MSG Engineering Ltd
Bibliography
- "A Switchable Four Element 80-Meter Phased Array", by Dana Atchley, W1HKK/W1CF, March 1965 QST.
- "Antennas and Techniques for Low-Band DXing", by John Devoldere, ON4UN.
- "The ARRL Antenna Book" by R Dean Straw, N6BV, published by ARRL.
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