The equisignal method of airplane signaling consists in receiving signals, sent out by one or more transmitting stations, alternately on two loops the planes of which differ by a certain angle. If the signals obtained on the two loops are equal in intensity, the bisector of the angle between the loops will correspond to the line of sight or of wave propagation. In the development of the apparatus described in this paper, the fundamental idea made use of was that of the old Telefunken compass, which was later used to a considerable extent by the German Navy during the war as an aid to the flight of Zeppelins in their raids on England, and in which the transmitting system consisted of a number of similar directional antennae that could be thrown into the circuit in succession and had directional effects differing in orientation by 10-deg. steps. To overcome the difficulty of keeping such an antenna system in balance, Bellini and Tosi in 1907 patented an antenna system consisting of two directional antennae set at right angles to one another and independently excited by a rotatable coupling-device known as a “goniometer,” the physical effect of which was the same as that of a large rotatable directional antenna or loop having the same dimensions as the two component antennae or loops, and which therefore served the purpose more simply and better than the Telefunken device. Use was also made of an idea contained in a German patent, which consisted in using two directional antennae, the planes, and therefore the directional effects, of which differed from one another by a certain angle and in sending out the letter n (- .) in Morse code on one antenna and the letter a (. -) on the other, it being evident that the two letters would be equally strong along a line bisecting the vertical planes of the two antennae in question. With such a device it would therefore be possible to determine the equality of the signals much more closely and easily than to determine the maximum intensity of a single signal. The radio beacon described in the paper is based on the idea of incorporating balanced signals into the Bellini-Tosi system, either to produce rotating equisignals, in place of the original Telefunken rotating signals, or to produce fixed equisignals in any desired direction, instead of along only certain lines depending upon the position of the originally constructed antennae or loops.
Reference is made to the various means of direction finding and their respective advantages and disadvantages, a brief history is given of the history of the development of the radio beacon, its mechanical parts are described, the theory of the goniometer and types of loops are discussed, the equisignal method of signaling is explained, and practical examples of flights are cited.


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