EARTH EFFECT

Radio Record, Volume I, Issue 14, 21 October 1927, Page 2

EARTH EFFECT

A FACTOR IN FADING CARNEGIE LINSTITUTION RiiSEARCH. Terrestrial magnetism as a possible cause of the fading of radio signals and the resistance of the ground to the flow of electricity as a reason for ‘unfavourable reception of programmes from some radiocasting statiens are wo interesting theories advanced by O. H. Gish, of the Carnegie Institution of Washington. Preliminary investigations undertaken by this scientific laboratory under the general heading, ‘Possible Relations Between Earth-Currents Earth-Resistivity, and Some Radio Phenomena,’ have been so promising of fruitful results as to warrant a continuation of the studies. Listeners who are subjected to the exasperating experience of the waning and waxing of signals while listening to a speech or musical concert would like to know whether or not ‘Mother Earth" is the offender due to earthcurrent manifestations occurring in conjunction with fading, as suggested by the Carnegie Institution .f Washington. Radio fans are likewise perplexed by the phenomenon of’ untavourable reception in certain directions from some stations and even frem all points of the compass with respect to a few transmitting stations. The probable explanation for this is that the ground at the surface of the earth sets up resistance to the flow cf electricity; hence, the Carnegie Ixstitution proposes a "‘resistivity-survey,"’ as applied to radio phenomena. "That ‘certain aspects cf thie earth’s electric currents ond «f radio —

phenomena may be related is suggested both by theory and by observational data,’? contends Mr. Gish, ‘‘although,’’? he continues, "it is not to be expected that this relationsnip is one of cause and effect, yet it is likely a sufficiently intimate cne to meke profitable a comparative study cf tlese two sets of phenomena. "Before the development «{ 1 ¢io, the conception of a region in the up- | per atmosphere highly capable ct conducting electricity was invoked as a necessary part of the mechanism giving rise to changes in earth-curruts and the earth’s magnetism. A similar condition of high conductivity in about the same region of atmospilere is now also demanded by some featries of radio transmission. It thus secims likely that the same conducting region affects both earth-currents end radio, and on that account certain consistent correspondences may Le expected between them. , bs "The data at present availabe for such comparison, though meagre, indicate that the daily as ‘veil a» the annual change in signal intznsitv for radio waves in the broadcast of frequencies is the reverse ‘ the change occurring in the earth-current activity. ‘hese as well as other soints of correspondence could be deduced from the correlations found by Dr. Greenleaf W. Pickard, of Boston, between the earth’s magnetic activity and variations in signal strength, for it is well ‘known that earth-currents and terrestrial magnetism are closely related. Furthermore, since good theoretical grounds now exist for expecting terrestrial magnetism to directly affect radio transmission, perhaps producing such phenomena as fading, one may also find earth-current manifestations occurring in conjunction ‘ with fading. na mime

y ‘"Atmospherics or static, that wellknown nuisance to the radio audience, is to the geophysicist an interesting phenomesion, deserving more of his attention than it has thus far received. This phenomenon has an apparent counterpart in earth-currents and makes itself most commonly evident on telephone lines, in which a ground return is used, preducing sounds in the receiver which resemble in a remarkable degree the clicks, .crashes, grinders, etc., which interfere with radio reception. | "Similar changes are probably occurring in terrestrial magnetism, but the magnetic instruments are not capable of responding to such rapid changes. ‘Ihe electrical effects can, however, be easily detected and even measured or photographically recorded without great difficulty, thus admirably supplementing the magnetic measurements, With ample measurements of these magnetic, earth-current and tadio effects over the same interval of time and in the same general region, doubtless much of both practical and theoretical value may be learned. "The resistance offered by the ground at the surface of: the earth to the flow of electricity also plays a part in the transmission of radio waves, and such knowledge of this property of the earth as may be ob- tained by ‘resistivity-surveys,’ similar to those made by the department of terrestrial magnetism of the Carnegie Institution of Washington as part of a study of earth-currents, would "oubtless indicate the reason for unfavourable reception in certain directions } from _ some broadcast stations and even in all directions from a few."