Design Considerations
Research2,3,4 indicated that efficiency of a shortened antenna could be improved by: 1) using a capacitance “top hat” sufficiently large to raise the radiation resistance; 2) using low loss coils; and 3) locating the loading coil near the mid-point of the shortened (40-meter) antenna wire.
Antenna efficiency is defined as the ratio of the radiation resistance to the total resistance, which includes ground losses. Radiation resistance is the antenna feed-point resistance caused by the radiation of electrical energy. The other system losses include loading coil losses at the transmission frequency, losses in the antenna wire, and return loss of the local ground. Raising the radiation resistance and reducing the other losses is the
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