Page:Wireless Telegraphy and Telephony (1908, Massie and Underhill).djvu/46

 

Chapter IV

Method of Operation

16. Switching Device

While, as before stated, in some cases separate antennæ are used for sending and receiving, it is common practice to use the same antenna for both. This is accomplished by means of a switching device so arranged that when the transmitter is connected in, the receiver is cut out. This is absolutely necessary, as otherwise the delicate receiving apparatus would be destroyed should the high-power currents of the transmitter pass through it.

17. Sending the Message

In Fig. 18 are shown several types of keys used in wireless telegraphy. The operator sends the message by pressing the key lever downward, or allowing it to remain up for certain periods of time. Pressing the key lever downward for a brief interval represents a dot, and a longer period of depression, a dash. The proper arrangement of dots and dashes forms letters, and combinations of letters of course form words, etc. the letters being

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