Page:Popular Science Monthly Volume 88.djvu/972

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��Popular Science Monthly

��the filament; and battery 31 supplies the telephone current through recording relay 31, telephones 40, discharging relay 51, ballast resistance 39 and plate 12 of the audion bulb. The contact of the discharging relay 54, may be arranged simply to short-circuit the condenser 25, or (as in Fig. i), actually to place upon it an opposing charge from battery 61, regulated by the potentiometer 60. The recording relay 32, -operates the sounder 34. It should be noted that both relays are of the back-contact type, which close their local circuits when the current through their magnets is reduced or interrupted.

The operation of the receiver, with weak or moderate incoming signals, is exactly like that of the simple audion. Unless impulses of sufficient strength to paralyze the tube are received, the relays do not close. As soon as a violent impulse arrives, however, the large positive charge assumed by the grid chokes off the flow of current from bat- tery 31, and the armatures of the two relays spring back and close their contacts.

The discharging relay reverses the grid charge and, in this way, permits the audion to regain its normal sensitive condition immediately; the recording relay causes a click of the sounder. Evidently the system of connections shown allows the reception of strong signals by listening to the sounder, yet prevents interruption of the receipt of messages of single violent impulses. It is, of course, necessary to adjust relay 51 to contact very quickly, so that the brief click caused by each closing will not interfere with the reading of messages.

The Non- Synchronous Rotary Gap

THE effectiveness of this popular type of gap depends mainly upon the adjustment of the electrodes and the speed at which the disk is driven. While with it, the absolutely clear note of the synchronous type cannot be obtained, the adjustment should be such that a comparatively even tone may be secured. The somewhat "raggy" spark given by this gap is not entirely dis- advantageous, as it is very efi^ective in working through certain kinds of static.

��With regard to the speed at which the disk should be driven: although a high speed will naturally increase the shrill- ness of the note produced, there is a considerable loss in radiation at very high speeds, owing to the fact that there is not sufficient time between the sparks in which to charge the condenser to its highest voltage. The use of too many points on the disk amounts to the same thing, and should be very carefully guarded against. — N. A. Woodcock.

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��A neat and complete record of messages received can be kept in this manner

A Wireless Log for the Amateur

THE experience of listening is much more valuable if a careful record is kept on some such log as that illustrated. The abbreviations used in the heading are translated as follows: Sta. Cld., sta- tion called; Pri., primary of loose-coup- ler; Sec, secondary of loose -coupler; Var., variable condenser; Clg., coupling. This log was used with a na\'y-type coup- ler, and complete entries made on the fol- lowing plan: For example, take the third note, in which N. A. A. was called by X. A. X.; the 12-9, under Pri., means that the best signals were received at the twelfth point of the multi-turn switch and the ninth point of the single-turn switch. The numbers, under Clg., give the length of the coupling in inches. In a coupler which has a slider instead of switches on the primary, the slider-rod may be calibrated. This simple chart is easily handled and from it many in- teresting observations can be drawn.

Quenched Gap Damping

A GOOD quenched gap set will give decrements as low as 0.03, for which value there are over 75 waves to the train.

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