944 



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. 



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. 



