File:Log periodic VHF TV antenna 1963.jpg

Summary

Early <a href="https://en.wikipedia.org/wiki/log-periodic_antenna" class="extiw" title="w:log-periodic antenna">log-periodic</a> <a href="https://en.wikipedia.org/wiki/television_antenna" class="extiw" title="w:television antenna">television antenna</a> used on the VHF TV channels 2-13, 54 - 216 MHz, from 1963. It consists of 11 <a href="https://en.wikipedia.org/wiki/dipole_antenna" class="extiw" title="w:dipole antenna">dipole</a> <a href="https://en.wikipedia.org/wiki/driven_element" class="extiw" title="w:driven element">driven elements</a> of gradually decreasing length, each consisting of a pair of aluminum rods. The dipoles are mounted in a line, attached to the feedline to the TV in parallel, with alternating phase. The log-periodic dipole antenna was developed by R. H. Du Hamel and Paul Mayes at the University of Illinois.around 1962 and immediately became popular as a rooftop television antenna. Previous high-gain rooftop antennas for fringe TV reception were based on the <a href="https://en.wikipedia.org/wiki/Yagi-Uda_antenna" class="extiw" title="w:Yagi-Uda antenna">Yagi-Uda antenna</a>. The Yagi has an inherently narrow bandwidth and could not cover the entire VHF band with flat gain. The log-periodic antenna was unique in that it could achieve as high gain as the Yagi over a broad bandwidth, and so could cover the entire VHF-TV band. Log-periodic antennas for VHF TV reception had V-shaped elements, as shown in this antenna. This was because on the high channels the dipoles resonated at their 3rd harmonic; they functioned as 3/2 wavelength dipoles. At these frequencies the main lobe of the radiation pattern of each element splits into two lobes at an angle to the rod axis. Slanting the two sides of the dipole in a V shape caused the main lobes of both sides to combine into one lobe, increasing the gain on the high channels.

Licensing

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