Text: A YAGI, or a log periodic, or a helical coil receiving antenna has a gain figure (amplification quantifier) in decibels, and 20 to even 50 db is quite possible with many such antennas. Try, for example, checking out the yagi antennas made by Mosley, the log periodics made by MilCom, the helicals made by Heli-Crafters. This means the passive antenna resonates and in effect amplifies an incoming signal as much a 100 or more times its incoming power level or signal strength while rejecting other frequencies. These passive antennas do not require any outside energy excitement to work as described, though there ARE active tunable antennas also. MFJ and others make antenna tuner/match boxes that are not powered but when connected to an antenna, even a long random length wire or even a wet string, electrically 'lengthen or shorten' an antenna to establish resonance at any frequency range. Bringing an antenna to resonance is a fundamental necessity to achieve maximum efficiency of an antenna in either passive or active mode of usage. The Amateur Radio antenna/tuner match box is the basis for the resonant tank circuit used on the TREC. The flat spiral antenna is based on a satellite microwave receiving antenna like used in GPS receivers, but adjusted in size to resonate at much lower frequencies closer to the standing waves generated by the Earth's magnetic field interacting with the charged ionosphere.

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