Page:Popular Science Monthly Volume 92.djvu/649

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Popular Science Monthly

��633

��Non-directional antennae

���Mechanica switch

��Section of Telefunken-compass sending station. Six- teen such sets form the aerial shown on page 632

��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 vVire connecting non-direction- ^ of fog or blind- a! antennae to switching ing storms. It machine V

is this appara- tus which has evidently been adapted exten- sively to war Zeppelins.

In wireless, parallel anten- nae give the strongest sig- nals; 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, de- termines the direction of the sender and thereupon transmits the information to the sender by radio. Under the Tele- funken plan, the moving station deter- mines its own position, powerful signals ha\ing been sent out from fixed stations along shore. This seems to be the better arrangement, as it is more practicable te have powerful stations on shore than aboard an airship. The signals can radiate out over longer distances, the sending station can be entirely autom.atic, and on board the airship the commander need only listen for loudest signals (or weakest, v.hichever 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 Ger- many 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

��fiashed 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 bi- plane, 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 appa- ratus is re- quired. How- e v e r a calibrated

��Cable connecting all directional antennae to switching machine

��pocket stop watch must be referred to. By "calibrated" we mean that the hand of the watch runs like the previously de- scribed 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 com- pass with the usual thirty-two points instead of with ordinary minutes and seconds.

��The plane de'lerminecl ^ N

���5topwatcK dia

Rotating switch at the sending sta- tion. It and watch -h and lineuptoindi- cate position

��At left is the one- handed watch comman- der on Zeppelin carries. Four sample positions shown. "Strong- est signal ' ' points to home station

��N Start

���5 Strongest signal ^

��signal

A^i^■onA^tic switch

��\

��Since commander's watch-hand and the send- ing switch rotate ?n unison, loudest signal determines plane in which sender is located

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

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