Page:Popular Science Monthly Volume 88.djvu/480

 452

marks are blotted from view by mists or fogs. The French government, as well, has made it possible for ships, fitted with the compass, to determine their positions through wireless signals from the stations along the coast.

The United States Radio Service is now experimenting with the Bellini- Tosi type of radio compass at Cape Cod and the Telefunken compass at Fire Island. The purpose of each is to en- able the navigating officer of a vessel to take bearings of wireless telegraph sta- tions, in order to find the position of his ship or to avoid collision with other craft. It is not asserted that the bear- ings taken exceed, or even equal in ac- curacy, those taken with an accurate op- tical instrument under favorable condi- tions, but reliable bearings may be obtained by radio, when direct optical bearings may not be taken because of unsettled weather, etc., and in making harbors, in keeping to difficult channels, and in avoiding collisions with other vessels, when fog obliterates surround- ing objects from view.

Transmitting Distributors of the Tele- funken Compass

Both compasses are modifications of the same principle. The Bellini-Tosi type provides that the moving station, whose position requires determination, shall send signals to a fixed station. The direction of receipt is determined at the fixed station, and then transmitted by wireless to the moving station. In the Telefunken system, the fixed station sends out signals and the moving station determines from what direction they are coming. In both arrangements it is necessary that one of the stations should be directive.

Directive sending is accomplished by special antennas, which are considerably more complicated than those of the ordi- nary undirective type, require greater space, and are difficult to install on movable stations, such as ships or aero- planes. The system in which fixed sta- tions send out directive signals, therefore, appeared most feasible to German in- ventors. In this case the movable re- ceiver need only be equipped with an ordinary antenna. The Telefunken com-

��Popular Science Monthly

��pass is so worked out, then, that it may be installed only on shore. Some thirty- two transmitting antennas are disposed at equal distances around a circumfer- ence of a circle 200 meters in diameter. Each pair is joined up successively with the transmitting apparatus by a rotary distributor, and at each position a signal corresponding to a point of the com- pass is sent out. An operator on board ship thus hears a succession of signals, increasing gradually in strength to a maximum and then dying away. The loudest signal occurs at the moment the shore operator is sending on the anten- nas pointed in the direction of the re- ceiver. All that is necessary for the ship operator to do, then, to obtain the bearing of the land station, is to note the signal that is strongest.

On the other hand, the Bellini-Tosi arrangement is contrived so that it may be installed on shipboard. The ship thus fitted is enabled to get its bearing from any wireless station on the coast or inland, if within range of the ship's wireless. The salient features of the Bellini-Tosi system are two aerial loops of equal size, suspended in vertical planes crossing each other at right angles, and a "radiogometer" or special receiv- ing transformer, having two primary coils of equal size and crossing each other at right angles in vertical planes. When a signal is received, currents are induced in both aerials, their relative strength depending on the direction of the sending station with reference to the planes of the two aerial loops. The signal is loudest when the plane of the aerial loop is the same as that of the sending station, weakest when the planes are at right angles. The induced cur- rents pass through the corresponding crossed coils in the instrument and pro- duce, in the space enclosed by them, two magnetic fields at right angles to each other. The two fields have relative strengths depending on the relative strengths, depending on the relative aerials, and they combine to form a re- sultant field at right angles to the di- rection from which signals are coming. The pivoted secondary coil will conse- quently receive the strongest signals when its plane is in the direction from which signals are coming. A pointer at-

�� �