Invelco AT-110 folded dipole antenna
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7. Results.
In this section I will analyse the results of the simulations made with the two models of the Invelco AT-110A antenna described on the section 2 and using 4Nec2. I have made a total of 408 simulations, counting the convergence and AGT tests and the simulations of SWR and radiation patterns for both models.
The results achieved with both models are quite similar, so the operators of this antenna can use either of them.
The simulations have been made considering the frequency range from 2 MHz to 30 MHz, installing the antenna in inverted-V configuration over an average terrain and using masts of 9 m, 12 m, 15 m and 18 m.
7.1. Standing wave ratio (SWR).
In both cases (model 1 and model 2), one can see the wideband behaviour of the antenna, with SWR values between 1,01 and 4,76 in the model 1 and between 1,03 and 4,22 in the model 2, all along the whole range 2-30 MHz. Analysing both plots one can conclude the following:
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The SWR is slightly worse in the lower frequencies.
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The SWR improves as the height of installation of the antenna increases.
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The lowest SWR values are seen around 6 MHz, 11 MHz, 16 MHz, 21 MHz and 27 MHz.
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The highest SWR values are seen around 3 MHz, 8 MHz, 14 MHz, 19 MHz, 24 MHz and 29 MHz.
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Being a wideband antenna, it is suitable to operate in automatic channel selection modes such as ALE.
Please note that those results may vary as a function of the environment where the antenna is installed (type of ground and nearby obstacles), so in every case it is advisable to use an antenna coupler in order to operate with the antenna. In ideal conditions, it may be enough using the internal coupler of the radio.
7.2. Radiation patterns.
In the simulations performed with both models, one can see similar results relative to the radiation characteristics of the antenna:
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Regardless the height of installation, the antenna is omnidirectional in frequencies between 2 MHz and about 7 MHz, presenting its maximum of radiation in a direction perpendicular or near perpendicular to the ground. This way, working in those frequencies, the antenna is suitable to establish NVIS links in mobile networks.
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In frequencies higher than 7 MHz the takeoff angle is lower, between about 10º and 60º of elevation depending on the height of installation of the antenna and the working frequency. The same way, the azimuth angle for the maximum of radiation also depends on the frequency and the height of installation. In previous sections you will find plots to make easier the process of pointing the antenna at the intended station for each case.
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Being common for HF wideband antennas of these dimensions, the AT-110A has losses in almost half of its working band (lower frequencies), a fact which may be taken into account when assessing the necessary transmission power to establish the links. Anyway, the necessary level of equivalent isotropic radiated power to establish NVIS links is not very high.
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In the lowest frequencies (up to about 7 MHz), the antenna gain is slightly better when installing the antenna with higher masts. There is no significant improvement in the higher frequencies.
Ismael Pellejero - EA4FSI |
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