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RADIO AGE for September, 1927
Radio Aids Air Mail
(Continued from page 24) zone in the direction of flight — when flying across the equisignal zone. The shift was greatest when the airplane was flown at right angles to the equisignal line. When flying to or from the transmitting coil the shift was not noticed.
The apparent displacement of the equisignal zone in the direction of flight was more marked the greater the altitude of flight. Twenty miles from the radio beacon station this shift at an altitude of 1,000 feet was found to be one mile; that is, an airplane flying in one direction across the equisignal zone found this zone displaced from its true position one mile in the direction of flight ; an airplane flying in the opposite direction found the equisignal zone displaced one mile in the new direction of flight. At 2,000 feet this zone displacement appeared to be 2 miles, and at 3,000 feet it appeared to be 4 miles. At all altitudes, however, with the airplane in a stall so that the trailing antenna hung vertically or when the airplane was flying toward or away from the beacon station there was no zone displacement, the zone being located in the position determined by ground tests.
"The result of these tests," indicated the Bureau of Standards, "in which a light antenna weight and a 200foot trailing wire were used, showed that the apparent shift in the equisignal zone was due entirely to the type of receiving antenna used and its inclination to the vertical. By using a short trailing wire with a much heavier weight the antenna hung in a nearly vertical position, thus eliminating the zone displacement effect to a large extent. Such an antenna is best suited for this type of reception, as any ambiguities arising from an apparent shift in the equisignal zone when the airplane is turned are practically overcome. The use of a coil antenna in place of a trailing wire is equally effective in this respect, but cannot be worked over as great a distance."
Of the future of this far-reaching system of guiding aircraft by slender beams of directed radio, Dr. Dellinger states :
"In carrying out its newly assigned responsibilities to provide aids to air navigation on the civil airways, the Department of Commerce has concluded that radio aids are indispensable. As the first step in establishing these radio aids the Bureau of Standards has been assigned certain research work and is setting up model installations.
"It has been established that the airways -must be provided with a
system of radio telephone transmitting stations and directive beacons at certain intervals. At smaller intervals between the directive beacon, probably every 25 miles, are to be located the marker beacons. It is not yet certain whether the beacons will operate by means of an audible or a visual signal on the airplane, and the determination of this is one of the principal objects of the investigations now in progress.