Paradigm Lost: Nikola Tesla's True Wireless Page 12

(which nowadays is called “an inverted L”) is just as effective as a receiver or transmitter as the straight antenna on the left. He claims that he has performed an experiment that supports this conclusion. He also asserts that the experiment proves that “currents propagated through the ground, and not … space waves” is the reason for true wireless telegraphy.

In 1919, an understanding of the theory of receiving antennas was still fairly primitive.²⁶ And it was only in 1924, with the work on reciprocity of John R. Carson at Bell Labs, that the tools that had been developed to analyze transmitting antennas could be brought to bear on receiving antennas.²⁷ So, we must not be harsh in condemning Tesla for his wrongful assertion. However, it was known as early as 1898 that if antennas are placed above a flat highly conducting earth, one can invoke the method of images for analyzing them.²⁸ It was well known before 1919 that if the earth is a good conductor, the electric field of a propagating radio wave would be primarily perpendicular to the earth, and the field strength would be proportional to an integral of the current along the vertical portion of the antenna.

It should have been apparent to Tesla that if a transmitting vertical wire antenna is small, measured in wavelengths, and has the shape of the antenna on the left of Fig. 6, and if it is now bent into the shape shown on the right, then the electric field normal to a flat highly conducting earth is reduced.²⁹ However, the situation here is potentially quite complicated. The difficulty occurs with an imperfectly conducting earth. Marconi, in 1906, described to the Royal Society an array he built consisting of inverted L antennas and observed that the array broadcasts most effectively in the direction of the arrow shown below, i.e., away from the horizontal element.³⁰ Fig. 7 is taken from Principles of Wireless Telegraphy by G. W. Pierce, published in 1910.³¹

Jonathan Zenneck, in the same era as Pierce, describes the work of H. von Hoerschelmann, a student of Arnold Sommerfeld, who apparently was the first to explain the directive properties of Marconi’s antenna. His earth is assumed to be imperfectly conducting. He includes the vertical portions of the current induced in the earth directly under the horizontal wires of the array.³² The upshot is that whether one assumes a highly conducting earth or one of imperfect conductivity (as is required for Marconi’s antenna), Tesla’s assertion “that the antennas can be put out of parallelism without noticeable change in action on the receiver” is utterly wrong. Marconi’s inverted L was constructed in the year 1905, and the explanation by Hoerschelmann was