Magnetic loop antennas have become popular in recent years as they solve many of these problems. Some locations will not allow antennas at all due to council or strata regulations or neighbour objections. A balanced antenna such as a dipole or beam will not perform well if it is much less than a wavelength above ground due to a high angle of radiation. If the antenna is much less than a quarter wavelength in height it will have low radiation resistance in the order of a few ohms and reduced efficiency when fed against a lossy ground. Even an extensive radial system may have significant earth resistance (20-30 ohms). An unbalanced antenna such as a vertical or long wire fed against ground will require a low resistance earth or radial system which may present its own problems. For the lower frequencies this is impractical for most domestic installations. They require towers or at least a support to allow the antenna to be a substantial fraction of a wavelength above ground. Magnetic Loop Antennas – a brief theory and a practical antenna for 3.5 to 14MHz ABSTRACTS u2013 2017 | 2018 by Marica Martella is licensed under CC-BY-NC-ND 4.0įor Radio Amateurs wishing to use HF bands below 30MHz, the physical size and height above ground of conventional antennas can be a problem.
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