RADIO COMMUNICATION 265 



The antenna is made and installed as follows. First decide 

 upon its location. The wire should be suspended between 

 two high points so that it does not come in contact with any- 

 thing between these points. The wire should be stranded if 

 possible and as nearly 150 feet long as the location will permit. 

 Attach to the end of this stranded wire, near that insulator which 

 is closest the set, an insulated wire which is led through a tube 

 insulator into the room where the set is located. Around the 

 groove in the knob insulator, or to the other end of the strain 

 insulator, attach wires or ropes and secure these to the high 

 points selected. For these points poles may be erected on the 

 roof of a building, or trees may be used. The antenna need be 

 only high enough to clear immediately surrounding obstacles. 



To adjust the set for receiving, fit the receivers to the ears 

 and adjust the whisker on the detector so that it just touches the 

 crystal lightly. Now move the sliders back and forth one at a 

 time until locations are found at which the signals are heard. 

 After a little practice the proper positions of the sliders will be 

 more readily located and it will be possible to adjust the detector 

 with greater nicety. 



A more elaborate and yet very simple receiving outfit is 

 shown in Figure 120 (p. 266). The difference between this outfit 

 and the one in Figure 118 is found in the substitution of a receiv- 

 ing transformer in place of the tuning coil and the addition of a 

 variable condenser. The receiving transformer consists of two 

 cardboard tubes each wound with a single layer of wire and 

 adjusted so that one will slide within the other. The wire on 

 both tubes is the same size. When a current flows in the circuit 

 from antenna to ground going through the outer coil, it induces a 

 current in the other coil whose strength depends on how far the 

 second coil is shoved into the first. The variable condenser 

 (Fig. 121) consists of two sets of metal plates, those of one set 

 alternating with and parallel to those of the other, to which they 

 lie very close without being in contact. One set, the rotor, is 

 so mounted that its plates may be moved so as to lie wholly or 



