Wireless Telegraphy and Telephony

CHAPTER II. THE MEANS FOR RADIATING AND INTERCEPTING ELECTRIC WAVES. AERIAL SYSTEMS. EARTH CONNECTION. Every radiotelegraphic station may be summed up as com- prising these elements: first of all, certain appliances col- lectively forming the transmitter and serving to create the waves; secondly, the receiving apparatus, whose function is to detect the signals of some far-distant sending station, and lastly, an external organ called the aerial, or antenna, con- sisting of a huge system of wires elevated high in the air above all surrounding objects, either vertically or sloping, or partly horizontal and partly vertical, which radiates or intercepts the electromagnetic waves, accordingly as the sta- tion is transmitting or receiving. The antenna is at once both the mouth and the ear of the wireless station. Its site and arrangement will greatly -determine the efficiency and range of the apparatus. The site selected is preferably such that the aerial will not be in the immediate neighborhod of any tall objects, such as trees, smokestacks,. telephone wires, etc., because such objects not only absorb an appreciable amount of en- ergy when the station is transmitting messages, but also noticeably shield the aerial from the effects of incoming signals and limit its range. The nature of the ground over which the waves must travel also enters into the question, and is always consid- ered in locating a station. In gliding over the surface of the earth, the waves generate weak currents in the earth 12