800 



Popular Science Monthly 



pany submitted a i -kilowatt set complete 

 which weighed lOO lb. Each of the 

 De Forest audion sets weighed 86 lb. The 

 Dubilier quenched arc set weighed 64 lb. 

 The three sets in question were given rigid 

 scientific tests, each manufacturer having 

 seen to it that his apparatus was abso- 

 lutely foolproof. 



Mr. Dubilier's system is particularly 

 interesting. Formerly Leyden jars were 

 broken and short-circuited. The entire set 

 was out of commission until the broken jars 

 could be renewed. Hence, warships, as 

 well as airships, were in danger when the 

 Leyden jars gave out. In the Dubilier 

 system, the secondary is not short-circuited, 

 whatever happens, but continues to work 

 uninterruptedly. Hence, it is practically 

 impossible to throw the set out of order. 



How to Make a Sending Oscillation - 

 Transformer for Wireless 



THE construction of the oscillation-helix 

 is shown in the illustration. The 

 heads of the primary or larger coil, are 



7 TURNS NO 8 



ALUMINUM WIRE 



A sending oscillation-transformer that will 

 prove valuable to any wireless station 



I in. thick and 12 in. in diameter, and are 

 held apart by four strips of wood 9 in. wide 

 and ^ in. thick, which are placed in ^-in. 

 notches in the disks as shown. This makes 

 the distance between the two heads 8 in. 

 The lower head is provided with three legs, 

 which may be made of fiber. Insulators 

 screwed to the bottom of the head will 

 answer the same purpose. A i-in. hole is 

 drilled in the center of each head to admit 

 a 15/16-in. dowel or a piece of curtain pole 

 of the same diameter and 26 in. long. 

 Several slots M-in. deep are sawed near 



the top of this vertical rod. A small strip 

 of brass is made to fit into any one of these 

 slots, the purpose being to hold the secon- 

 dary in place after the proper coupling 

 between the primary and secondary has 

 been determined. 



When all of the parts of the primary have 

 been assembled, it is wound with 7 turns 

 of No. 4 aluminum wire as shown. The 

 secondary, or smaller coil is next made, 

 the heads being 8 in. in diameter with a 6-in. 

 space between them. It has four uprights 

 which are notched into the upper and 

 lower heads in the same way as in making 

 the primary. The heads of the secondary 

 are drilled centrally to admit the dowel. 

 When the secondary has been assembled it is 

 wound with 11 turns of No. 8 aluminum 

 wire. The strip A , which holds the secon- 

 dary in position, is made from a piece of 

 1/16 in. copper or brass 2)^ in. long and 

 I in. wide. One end of the strip is drilled 

 for a small handle while the other end is 

 drilled to admit a screw that holds the strip 

 on top of the secondary. 



The oscillation-transformer will be a 

 valuable addition to any wireless station 

 and will help comply with the wireless law 

 regarding pure waves and wavelengths. It 

 can be used with a transformer up to and 

 including i K. W. input, and has just the 

 right amount of inductance in the open and 

 closed circuit sides to permit a range of 

 periods well above and below 200 meters. 



Testing the Sensitivity of the 

 Telephone Receiver 



AVERY simple experiment illustrating 

 the extreme sensitivity of the ordinary 

 telephone receiver may be made as follows : 

 Connect each terminal with about 2 ft. of 

 magnet wire of small enough gage to be 

 easily handled. Connect the free end of 

 one wire to a small scrap of clean sheet zinc. 

 Then while the receiver is held to the ear 

 with the left hand, moisten the end of the 

 other wire on the tongue and touch it to the 

 scrap of zinc. Immediately a definite click 

 will be heard in the receiver, thus register- 

 ing the infinitesimal current generated by 

 this minute galvanic battery. 



Most amateurs fail to appreciate the 

 value of the watch-case receiver in testing 

 for leaks and short-circuits, and accordingly 

 resort to magnetos or galvanometers which 

 are not nearly so sensitive, as a rule. If 

 you have a galvanometer subject it to the 

 above test. — ^John D. Adams. 



