950 



Popular Science Muiilldy 



transmitter. The simplest way to do this 

 is to connect a small single-pole switch 

 (either a knife-switch or a lever-switch of 

 almost any sort will do) directly across the 

 terminals of the detector. In the wiring 

 diagram of the complete station, Fig. 2, 

 the tlctector-protecting switch is marked 

 S; the wires leading from it to the Ijinding 

 posts of the detector should l)e kept as 

 short as possible; otherwise they may pick 

 up enough current from the sending-spark 

 to "knock out" or destroy the sensiti\e 

 adjustment of the crystal-detector. Wiien 

 receiving, the protecting-switch 5 must be 

 open, so that the detector can operate to 

 rectify the currents [jroduccfl in it by the 

 incoming waves. When sending, the switch 

 must be closed. In this position the heavy 

 induced currents are shunted past the 

 detector and the adjustment is not dis- 

 turbed by them. 



Connecting the Complete Set 



In addition to the parts of the receiving 

 station fully described in last month's 

 article, the various elements of the trans- 

 mitter illustrated and discussed in October 

 will be needed for a complete sending and 

 receiving station. In fact, a complete set 

 of parts is necessary for each terminal of 

 the proposed wireless "line." The following 

 must, therefore, be at each plant: 



Station: 



1 Antenna and support See September and 

 October articles. 

 I Loading Coil " October article. 



I Ground Connection " September " 

 I ChanRC-Over Switch " above. 

 Necessary wire for connections. 



Sender: 



I Set of dry or storage- 

 cells See October article. 

 I Sending Key " 

 I Induction Coil " " " 

 I Spark-Gap " " " 



Receiver: 



I Crystal- Detector See above. 



I Stopping-Condenser " " 



1 Pair of Telephones " " 



I Test-Buzzer " September article. 



I Strap-Key " " 



I Dry Cell 



I Uetector-Protecting 



Switch " above. 



The above-named elements of the com- 

 plete station must be carefully connected 

 together as shown in Fig. 2. It is a good 

 plan to use No. i6 or No. i8 lamp-cord for 

 the wiring of a set such as this. The 

 twisted pair should be separated and 



smoothed out, and the single conductors 

 used independently. 



It is necessary to keep the transmitting 



TLrTf-Js^^t 



5;.. GROUND 



FIG 2 



SENDING KEY 



The wiring diagram of a complete station 

 showing the location of wireless apparatus 



apparatus well away from the receiving 

 instruments. The loading coil, for example, 

 should not be nearer than two feet to the 

 detector, telephones and stopping-conden- 

 ser. As explained in the second article of 

 this series, the lead-wire from the loading 

 coil out to the aerial must be well insulated 

 if good work is to be done. It is very 

 important that the change-over switch be 

 well insulated, also, for three of its contacts 

 arc subjected to the full sparking potential 

 of the transmitter (see the diagram of 

 Fig. 2). 



The best plan for beginning work is to 

 have the two antennas, one at each station, 

 as nearly alike as possible. If their form 

 and height cannot be made identical, they 

 shotild at any rate have exactly the same 

 length of circuit. That is to say, there 

 should be the same number of feet measured 

 from the ground connection tij) through 

 the spark-gap (but not through the loading 

 coil) to till' distant insulated end of the 

 antenn.i, within a few per cent. In this 

 case, i. e., with the lengths practically 

 identical, the loading coils at the two 

 stations can be put entirely in circuit, and 

 the app.irattis will be approximately tuned 

 for the interchange of messages. 



If one of the aeri.ils is longer than the 

 other, less of the loading coil should be 

 used at that station than at the other. 

 Tlu' I'xact point to clip on to the wire of 

 the loading coil can be determined only 

 by exi)erinunt. By tr>ing every turn, it 

 will be found that some one position is 



