Popular Science Montlily 



457 



ters, sent simultaneously on the same 

 wavelength. Each sender used a diiier- 

 ent spark fre- 

 quency, and three 

 banks of relays, 

 such as those de- 

 scribed, were con- 

 nected in the tele- 

 phone circuit of 

 the receiver. Each 

 o f the relay- 

 groups was me- 

 chanically tuned 

 to the tone-fre- 

 quency of one of 

 the senders, and 

 therefore re- 

 from that station 



Fig. 2. An audion bulb 

 of high voltage 



sponded to signals 

 only. 



The use of group-frequency tuning, in 

 addition to the ordinary wavelength tun- 

 ing, gives a vast number of combinations 

 for the reduction and prevention of in- 

 terference. The practical difficulty is 

 that "static" is amplified along with the 

 messages, and, what is most unfortunate, 

 produces a ringing, musical sound. This 

 of course makes it all the harder to read 

 the signals. 



Patent No. 1,129,942, 1915, issued to 

 H. D. Arnold, shows a form of audion 

 tube of increased efficiency. It is found 

 possible, by varying the location of the 

 plate with respect to the grid and fila- 

 ment, and by altering the form of the 

 grid, to build audion amplifiers in which 

 the magnified en- 

 ergy is character- 

 ized either by 

 high voltage or 

 high current. A 

 bulb of the high 

 voltage type is 

 shown in Fig. 2, 

 in which the grid 



3 consists of fine 

 wire and is placed 

 close to the fila- 

 ment 5. The plate 



4 is set at some 

 distance from the grid-filament system 

 and the whole is enclosed in the usual 

 evacuated bulb 6. The patent referred 

 to deals especially with various coml)i- 

 nations of these high and low voltage 

 amplifiers for line telephony; neverthe- 

 less, the use of similar instruments for 



Fig. 3. A quenched spark 

 gap of unusual construc- 

 tion 



both radio transmitters, amplifiers and 

 receivers makes the design of interest. 



A quenched spark-gap of unusual con- 

 struction appears in Fig. 3. Small 

 tungsten buttons, having parallel faces, 

 are set into brass or copper electrode- 

 holders, and set with their parallel faces 

 very close together. A number of these 

 gaps, each operating in open-air, are 

 connected in series to make up the com- 

 plete quenched-gap system. With gaps 

 of this type, on account of the very high 

 melting point of tungsten, the two elec- 

 trodes can be adjusted very close to- 

 gether without any great likelihood of 



Fig. 4. Diagram of the shpping-contact de- 

 tector for radio telegraphy 



short-circuiting through oxidation. Also, 

 since tungsten is practically unburnable, 

 the diameter of the electrodes may be 

 made very much less than in the ordi- 

 nary quenched gaps. The inventor states 

 that little difficulty is experienced in get- 

 ting pure spark-tones when the tung- 

 sten electrodes are used, because of their 

 constancy in operation ; it is pointed out 

 that even with incorrect coupling values, 

 the spark tone remains good. Oscillation 

 circuit couplings of as high as 45 per 

 cent, giving extremely high quenching, 

 may be used. The drawing is taken 

 from 1915 U. S. patent No. 1,152,272, is- 

 sued to H. Boas. 



