Page:Popular Science Monthly Volume 92.djvu/649

 Popular Science Monthly p. 633

On page 451 and following of the March 1916 number, Popular Science took up and discussed at considerable length two radio directional systems, the Bellini-Tosi and the Telefunken, by which ships at sea could find their way along coasts and into harbors in spite of fog or blinding storms. It is this apparatus which has evidently been adapted extensively to war Zeppelins.

In wireless, parallel antennae give the strongest signals; those at right angles, the weakest. It is this principle which makes all radio direction-finding possible.

In the Bellini-Tosi system the moving station sends signals to a fixed station, and the fixed station, by special apparatus, determines the direction of the sender and thereupon transmits the information to the sender by radio. Under the Telefunken plan, the moving station determines its own position, powerful signals having been sent out from fixed stations along shore. This seems to be the better arrangement, as it is more practicable to have powerful stations on shore than aboard an airship. The signals can radiate out over longer distances, the sending station can be entirely automatic, and on board the airship the commander need only listen for loudest signals (or weakest, whichever he prefers), hold a one-handed stop-watch—hereafter described—in his hand, and he gets his direction almost at once. No doubt the many war Zeppelins which have ventured out over England have used this system. Details of the whole plan are interesting.

The powerful sending stations in Germany have thirty-two very long, slanting antennae radiating from a tall central mast. These antennae are the exact equivalents of the rays to be found on every ship's compass, and, like them, represent the thirty-two fixed points of the compass. A mechanically operated switch connects with opposite pairs of these separate aerials once every thirty seconds. A single telegraphic dot is flashed out at each connection. In this way all points of the compass are reached every half-minute.

Any German aircraft, whether it is a Zeppelin or a small reconnaissance biplane, is able to pick up these dots, and by this means it can determine its direction relative to the sending station. No other addition to its regular receiving apparatus is required. However a calibrated pocket stop watch must be referred to. By "calibrated" we mean that the hand of the watch runs like the previously described switch, and that it makes a complete revolution around the dial in thirty seconds. The dial is, of course, marked like that of a navigator's compass with the usual thirty-two points instead of with ordinary minutes and seconds.

Apparently the Zeppelins using the Telefunken-compass are equipped with ordinary non-directional aerials for receiving the signals.