Popular Science Monihhi 



445 



A New Tuner Arrangement 



IN building an inductive coupler, the 

 problem of reducing the usual number 

 of taps and switch points without losing 

 flexibility of adjustment was solved as 

 outlined below. 



The instrument was designed to be 

 a cabinet set. Since the space available 

 within the case was rather limited to 

 use, a sliding secondary coil was im- 

 practical. Hence the "static" type was 

 adopted. Primary and secondary coils 

 were wound on tubes of the same 

 diameter and placed at right angles to 

 each other to prevent induction between 

 them. Both cylinders are 8 ins. long and 

 3,1 2 ins. in diameter. The primary is 

 wound with No. 26 enameled wire, 

 tapped at every 22nd turn, 18 taps in 

 all. The secondary is wound with No. 

 30 enameled wire, tapped at ever>' 35th 

 turn, 18 taps in all. 



To permit of sharp tuning in the pri- 

 mary circuit, a small variometer was 

 constructed. The maximum inductance 

 of this is slightly more than a one-point 

 variation on the primary switch {22 

 turns). Hence with the variometer 

 connected in series as shown, even 

 sharper tuning can be accomplished than 

 with a tuner tapped to single turns. A 

 variable condenser of .0005 mf. is shunted 

 across the secondary for the close tuning 

 of that circuit, and a second variable 

 condenser of .001 mf. is connected be- 

 tween the primary and secondary coils, 

 which latter controls the coupling be- 

 tween the tw'o. The entire set is wired 

 according to the diagram. Comparative 

 tests with other instruments have proven 

 that the hook-up here described brings 

 in strong signals and permits of sharp 

 tuning. — Edwin L. Powell. 



Leader 



Variometer 



^h^-4im i 



D 



15 



® 



Diagram of the Wiring in the Construction 

 of a Tuner Cabinet Set 



Lepel Improves His System 



AN important 

 1916 patent is 

 number 1,168,837 

 issued to V.. von 

 Lepel for a method 

 of producing elec- 

 trical oscillations. 

 The drawing is a 

 reproduction of one 

 of the eight circuit 

 diagrams shown, 

 and is typical of 

 the invention. A 

 direct current gen- 

 erator 2 supplies 

 power to the con- 

 denser I through 

 impedances 7 7 and 

 resistances 6 6. The 

 discharge of the 

 condenser i takes 

 place through the 

 primary of oscilla- 

 tion transformer 5 

 and across the 

 parallel -plate 

 quenched spark- 

 gaps shown at 12. 

 The antenna and 

 ground are connected to the terminals of 

 the secondary of transformer 5. 



If the constants of the circuit are 

 properly chosen, according to the theory 

 which is explained in detail in the 

 patent, the combination of the quench- 

 ing spark-gaps with the "inertia coils" 

 will result in an arcless discharge in the 

 oscillation circuit, and the production 

 of practically perfect sustained oscilla- 

 tions in the antenna circuit. When it is 

 desired to telegraph by radio according 

 to the tone method, an auxiliary tuned 

 low-frequency circuit 15 is inserted as 

 shown, its natural frequency being that 

 of the note which it is desired to produce 

 at the receiver. The effect of this added 

 circuit is to reduce the amount of out- 

 going radiation periodically. 



By combining several values of induc- 

 tance and capacity in the tone-control- 

 ling circuit, and connecting them with 

 a group of keys, it has been found 

 possible to produce tones of the musical 

 scale and to transmit musical airs by 

 wireless over a long distance . 



One of the Eight 

 Circuit Dia- 

 grams of the 

 Lepel Patent 



