Page:Popular Science Monthly Volume 89.djvu/459

 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

�� �