Popular Science Monthly 



629 



Fig. 5. 

 Fig. 6. 



The Aerial 



The law.s permit amateur wireless 

 stations to use any wavelcngtii up to 

 200 meters, provided tiiat the wave sent 

 out is sharp and pure. This means that 

 the aerial wire system to be used with 

 t he sendinij appara- 

 tus described must 

 not be more than 

 7 5 ft. ! o n p , 

 measured along the 

 conductor from its 

 top to the ground 

 connection. It is 

 a good plan to use 

 two wires about 

 50 ft. long running 

 side by side to the 

 top of a tree or 

 chimney or special- 

 ly built pole, keep- 

 ing the wires about 



five feet apart by fastening them at each 

 end to a light wooden spreader. The top, 

 and in fact the whole aerial, must be 

 thoroughly insulated, if good results are 

 to be secured. An excellent plan for 

 preventing electrical leakage is to con- 

 nect in series, with loops or rope, 

 five or six porcelain insulators of the 

 kind used in building the loading coil 

 (Fig. 6). These are inserted between the 

 spreader which 

 carries the antenna 

 wires and the rope 

 halyard which is 

 used to haul up the 

 aerial. Similar 

 strings of insulators 

 must be used to 

 guy out the bottom 

 of the aerial. Where 

 the lead-wireenters 

 the house and con- 

 nects to the instru- 

 men ts it should 

 pass through a 

 thick porcelain 

 tube, as shown in 

 Fig. 7- 



The ground 

 connection may be made by wrapping 

 several turns of bare copper wire tightly 

 around a scraped water or steam-pipe. 

 The connection should be made at 

 a point near to the sending instru- 

 ments. 



SPREADER 



Type of porcelain insulators 

 The insulators connected in series 



LQftOING 

 COIL 



SPARK GAP 

 FI6.7 



Manner of connecting the several instruments 

 making up the complete sending set 



If no water pipes are available, a large 

 copper or iron plate may be buried 

 deeply in moist cartii. As a rule, 

 though, such earth connections are not 

 as satisfactory as a pipe forming part 

 of the town water system. 



Connecting the Set 



Theseveral 

 instruments mak- 

 ing up the complete 

 sending set must 

 be connected up 

 as shown in Fig. 7. 

 The spark-gap 

 should be adjusted 

 with its electrodes 

 quite close together 

 ■ — never more than 

 y^ in. apart and at 

 least half of the 

 loading coil is to be 

 put in series with the antenna. Unless a 

 large part of this coil is used the trans- 

 mitter will not radiate pure, sharp waves, 

 and its use will violate the law and make 

 its operator liable to prosecution by the 

 government. If the spark-gap is kept 

 short and a considerable portion of the 

 loading coil used, there will be nothing 

 to fear so long as neither of the aerial 

 wires is over 75 ft. in length. 



Whenever the 

 key is pressed, if 

 the set is properly 

 connected and ad- 

 justed, a bright, 

 snappy, singing 

 spark will jump 

 across the gap. 

 Each spark starts 

 a train of high fre- 

 quency currents 

 oscillating back and 

 forth in the aerial 

 wires, and a train 

 of electromagnetic 

 waves is radiated 

 into space. A suit- 

 able wireless 

 receiver located 

 where a (jortion of these radiated waves 

 will reach it, will pick up some of their 

 energy and produce from it a sound 

 which, indicates the dot-and-dash buzzes 

 of a Morse signal. 



( To he continued) 



GROUND 



