Fading and "Dead Spots"

Radio Record, Volume III, Issue 24, 27 December 1929, Page 27

Fading and "Dead Spots"

Research in the Antarctic

A" the present time a series of tests is being jointly carried out by. station KDKA, Pittsburgh, America, and the Byrd Expedition in the Antarctic, with a view to securing a better understanding of one of the most mysterious phenomena connected with radio "biind spots" or "dead areas." There are many small areas throughout the world where certain broadcasting stgtions can be heard only with diffie , if at all, although the same stations are quite clearly received all around these areas. While some of these "dead spots," as these areas are called, are caused by peculiarities of land configuration, others cannot be explained away so easily, and many scientists believe that the trouble is chiefly due to the so-called "Heaviside layer." The "Heaviside layer," according to theory, is a stratum, possibly magnetic in character, which surrounds the earth. -Radio waves normally do not pass through it, but are reflected back to earth by it, just as light rays are reflected by a mirror. In some places, waves thus reflected are the ones chiefly received, and this applies especially to long-distance broadcasting; at other places, the waves sent out directly by the%ransmitter are the ones that convey the messages; but in certain places ‘both sets of waves are received together, and it is thought to be due to the interference of these two sets that dead spots, and possibly fading, are caused. ° Tests indicate that the Heaviside layer encircles the earth at an average height of approximately 250 miles, but there is reason to assume that at either the North Pole or the South Pole, or both, this layer approaches close to the earth, or perhaps actually touches it. Definite confirmation or refutation of this theory is the object of these tests. . These are being sponsored by the United States Navy, not merely in the interests of pure science, but also for

purposes of national defence. It is. curious to note that dead spots ‘occur on sea as well as on land, and in time of war these areas would seriously interfere with naval operations. The investigation in the Antarctic is being carried out. with the aid of an instrument known as the "Osiso," invented by the late Mr. J. W. Legg. This makes photographic records of radio signals and other electric waves, and is so sensitive that it will measure time differences of only a few millionths of a second. By means of the Osiso records can be made of the reception of both direct radio signals and _ their echoes, as reflected by the Heaviside layer, and by measuring the time difference between them it will be. possible to determine the height of the Heaviside layer near the South Pole. Mr. Hanson, the radio expert accompanying the Byrd expedition, has already accomplished a. considerable amount of experimental work along this line, and he recently took a ten-mile trip out of camp with two companions in order to continue his investigations. Hanson carried the Osiso on his back and packed the necessary dry batteries inside his shirt to keep them from freezing. . : On his return from this trip he transmitted the following message to New York :-"Osiso giving splendid results in temperatures down to 70 below zero ‘with ski and knapsack and dog-sled transportation. Suggest KDKA ° cooperate oscillographie study by sending special signals to us, co-operating with Dr. Taylor, of Bellevue." The KDKA experts, having received Dr. Taylor’s suggestions, arranged with Mr. Hanson to send him a long, powerful signal, on exactly 25.4 metres, which enabled him to make more accurate measurements than was possible with ordinary radio signals. It is confidently expected that these investigations will reveal hitherto unknown causes of many phenomena eonnected with radio transmission and reception.