Underground Antenna

Radio Record, Volume III, Issue 20, 29 November 1929, Page 12

Underground Antenna

Proof of I nefficiency JN localities where the erection of an aerial is impracticable or impossible, and where an indoor antenna is undesirable, somewhat mediocre results may be obtained from a powerful receiver by the use of what is known as a "ground" aerial. This consists, in the main, of a wire buried underneath the surface of the ground, and well-insulated from the earth which surrounds it. The resulting reception is very poor, and nowise justifies the grossly exaggerated claims made by several American firms marketing a device known as an "earth antenna," an apparatus which is stated to function efficiently as an aerial while buried underground. ---"

In view of this, it is interesting to note the proceedings taken by the American postal authorities against some six companies who were marketing these devices per medium of the post. The following facts developed by the Postal Department serve to illustrate the type of advertising favoured by these companies. "It has been found that certain companies are obtaining remittances of money through the mails upon representations to the effect that for such remittances they will furnish a so-called underground antenna; that wlen used with radio receiving sets as directed, such antenna causes a miraculous reduction in static and noisy interference and gives clear-toned reception on every station which can be found; that such device is the ‘latest step’ in radio progress; and that the price of the device will be refunded at once, in full, to purchasers thereof who find the same unsatisfactory and return it." A so-called "earth antenna," together with the directions for use, were obtained from the promoters of the enterprise by the post office inspector who investigated this case. The device itself is cylindrical in shape, approximately thirteen inches in length and four inches in diameter, and is encased in cardboard at the sides and bottom. The top is sealed with a tarlike preparation, from which protrudes a wire approximately thirty-two inches

long enclosed in a lead cable. Attached to the outside of the device and running its entire length is a metal bar one half-inch in width and approximately 1-64th of an inch in thickness. Inside the device is a hollow core about which are wrapped. a number of windings of 4in. metal tape. The earth antenna and the directions were forwarded to the United States Bureau of Standards for examination and report. An exhaustive series of tests was conducted over a period of three weeks with the assistance of various ‘instruments for measuring with scientific accuracy the results obtained. A report covering. the results of these tests prepared by the expert was offered in evidence at the hearing and in addition he himself was present and testified. His testimony shows that the signals obtained by use of the earth antenna are inferior in strength to those secured from a vertical aerial in the ratio of from one to one hundred to one to several hundred. Results secured through use of the earth antenna were inferior in strength to those obtained by use of an ordinary two-inch pipe driven four feet into the ground in the ratio of one to fifteen. According to the statements of this expert, while it is true that a certain reduction in static is obtained by use of the earth antenna. a (directly proportionate reduction in general reception is concomitant thereto. Static was in fact present during certain of the tests when no other sound was audible. ) He stated in effect that any results "

whatever obtained from use of the earth antenna are due to the fact that it acts in some slight degree as a grounding device. 7 He further stated that while in some instances, due to improper installation of overhead aerials, lack of proper tuning of the set or similar factors, use of the earth antenna may seemingly cause.an improvement in reception, the fundamental fact remains that in passing through the earth electro-magnetic waves are greatly attenuated. Summarising his testimony, the expert stated that the earth antenna does not cause a reduction in static and noisy interference; it does not give "clear-toned reception’ on every station which,can be found or cause any kind of broadcast to be more faithfully reproduced; and it is not the latest step in radio progress. a" As a result of the proceedings tuted, a postal fraud order was issued by the Post Office authorities against the six companies involved. The above case should dissuade any radio amateur from installing a ground aerial in the hope that static will be reduced and reception improved.