FIG. 97.—Bellini-Tosi radio-goniometer for directive wireless telegraphy.
Another method devised by Braun employs two or more aerials at certain distances apart. The alternating currents used to excite the oscillations differ in phase, i. e. are so arranged that they have different comparative values at the same moment. It is possible to send very strong signals in a direction lying in the same plane as the aerials. By the use of three or more antennae suitably differing in their phase of excitation and situated at the vertices of a triangle it is possible to send strong signals in certain directions only.
FIG. 98.—Arrangement of Bellini and Tosi for directive wireless telegraphy.
Messrs. Bellini and Tosi have devised a very ingenious method of directively transmitting and receiving electric waves as shown in the accompanying diagrams. The antenna consists of two closed or nearly closed circuits of triangular shape arranged in two perpendicular planes. The two aerials each contain a circular coil of wire perpendicular to each other with their windings in the planes of the antenna circuits respectively. A third coil is connected to the receiving apparatus when the messages are incoming and to the condenser, spark gap and coil when the signals are to be transmitted.
Waves coming in from any particular direction produce oscillations in the two aerial circuits whose intensity varies according to the direction in which the waves These currents passing through the coils generate a magnetic field having a direction perpendicular to that from which the waves come. The strength of the currents in the movable coil will depend upon its position in the resultant magnetic field and will be at a maximum when the coil embraces as many as possible of the lines of magnetic force.
FIG. 99.—Complete receiving and transmitting outfit.
By providing the movable coil with a pointer it is possible to thereby determine the plane in which the station producing the signals lies. Any ambiguity regarding the final position of the station, whether it is located in the same direction indicated by the pointer or in the opposite one, is only removed by general knowledge of the location of existing stations.
The processes involved in sending messages are the reverse of those entering into the receiving apparatus. The movable coil being connected with the condenser, gap and transformer or induction coil creates a magnetic field which induces oscillating currents in the other two coils and consequent waves in the aerial whose strongest exertions will lie in a plane determined by the third coil. Changing the position of the latter will send the messages in any direction desired.