Page:Popular Science Monthly Volume 91.djvu/171

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Popular Science Monthly

Japan's Commercial System of Wireless Telephony

ALTHOUGH it is not generally realized, i Japan has been one of the most diligent countries in making wireless tele- phony a commercial possibility. The "T- Y-K" radiophone system which the Japa- nese have developed is unusual in simplicity and compactness. It contains no very intricate circuits, nor does it use a delicate air-sealed spark-gap, as in other telephone systems. The few adjustments that are necessary can be made by almost anybody, and the spark-gap will work while exposed to the air, without deterioration. These facts have .made the system so practical that Japan has already established wireless communication between her important islands by means of it.

The spark-gap electrodes are made of oxide of iron, brass, aluminum, and similar materials which are practically indestruc- tible. The electrode surfaces are small and are placed nearly

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��talking into the microphone transmitter.

But all this depends upon the formation

of a first spark which will release the charge

of the oscillating circuit. The resistance

���Ground '

��Diagram of connections: The transmitting system uses an air-exposed spark gap. A crystal detector system is used for receiving

��touching each other, so that the spark- producing potential can be comparatively low. Thus, the volt- age of the exciting generator is slightly more than one hun- dred, though as much as five hun- dred volts have often been used. As soon as a potential is pro- duced across the gap, an oscillating circuit that is coupled to the gap becomes simultane- ously charged. Once a spark jumps across the gap, the natural tendency of both the inductance and the capacity of the oscil- lating circuit is to send a current from one to the other. The result is that each is rapidly charged and discharged, the current crossing the gap at a rate of about 120,000 times a second, producing one spark with every surging. The surgings in the primary circuit are then induced in the aerial and microphone circuit which is coupled to it. The result is that the aerial radiates its wireless waves, which are modulated by

���between the two electrodes — caused by the insulating layers of air and of the oxide formed on the electrodes — ordinarily pre- vents this. So an equilibrator is used for temporarily raising the potential in the spark-gap circuit. The equilibrator con- sists of a strong electromagnet which, just as soon as a current begins to build up in it, attracts the armature of a circuit-breaker. The circuit-breaker is sharply opened, and the inductance discharges at high potential, supplying the necessary potential across the spark-gap.

Since the equilibrator works auto- matically, only the simple adjustments of the oscillating circuits require attention. The waves the system sends out, being of relatively low frequency, can be received by the ordinary crystal detector. Using it, a maximum range of thirty to forty miles has been obtained.

��A complete Japanese T-Y-K installation

��A Crystal Detector Holder for Wireless Apparatus

A SIMPLE clip to hold the mineral con- sists of a straight piece of brass sheet- ing with a U-shaped piece of spring brass soldered on at one end. Another and better device for holding the mineral is a reflector from an old tubular flashlight of the larger size. Clean off the enamel and polish up the brass. Fit a piece of wood into the socket and drill a hole in it for a ma- chine screw which passes through into the base of the detector. A large brass washer will be required under the head of the machine screw. Drill and tap out three holes through the side of the cup for the set screws which clamp the mineral. The cup will hold odd-shaped minerals of various sizes and can be turned around at will.

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