274 



Popular ScieJice Monthly 



tioiis, and in it is shown a complete 

 transmitter. Power is conveyed from 

 the generator ii, of approximately 500 

 cycles, to the transformer primary 19 

 by way of the signaling mechanisms 

 controlled by sending keys 17 and 23. 

 In the first of these a direct current 

 from battery 16 energizes the magnets 

 of relay 12, 13, 14, whose contacts 

 short circuit a portion of the impedance 

 18, 18' (which is shown as a trans- 

 former with the secondary arranged to 

 be shunted by the relay) and thus 

 allow the main current to pass. Wind- 

 ings on the relay 

 contact-arm prevent 

 it from opening until 

 the alternating cur- 

 rent passes through 

 zero amplitude, and 

 thus sparking is 

 avoided. The alter- 

 native method of 

 signaling is by key 

 23, which in its lower 

 position neutralizes 

 the impedance of 

 coils 21 and 22 by 

 closing a differen- 

 tially-wound sec- 

 ondary circuit 21^ 

 22' and so provides an unobstructed 

 path for the main primary current. 



The 500-cycle potential from the 

 secondary of the power transformer 19' 

 charges the main condensers 20 through 

 the choke-coils 47, 48. F"rom the con- 

 densers the circuit {)asses through sta- 

 tionary electrode 38, across one spark- 

 gap to the rotor 41 and then back to a 

 second stationary electrode 39. From 

 here the primary oscillations are led 

 through the transformer coil 28 and 

 back to the condenser. The secondary 

 28' is connected to antenna 26 and 

 ground 29 in the usual way, and the 

 ammeter 27 is inductively coupled to 

 the antenna circuit. A protectixx- spark- 

 gap 35 is connected across the main 

 rotary gap, so as to prevent damage 

 from excessive potentials. With con- 

 nections as outlined, if the rotary gap is 

 I)rovided (as shown) with one si)oke for 

 each pair of field poles in the alternator 

 upon whose shaft il is mounted, there 

 will occur oidy one spark for each 

 complete cycle of alttrnating current. 



A radio transmitter suitable for sending 



messages on half power by using the lower 



spark frequency 



If, howe\er, a second pair of stationary 

 electrodes 37 and 40, spaced exactly 

 half-way between the first pair (as 

 regards the electrical cycle), are con- 

 nected into circuit, there will be a spark 

 for every half-cycle. That is to say, by 

 connecting the additional electrodes into 

 the primary oscillation circuit there are 

 given twice as many opportunites for 

 sparks to pass. The change in connec- 

 tion may be made by moving key 25, 

 which controls the output of battery 24 

 and thus operates relays 36 and 30. 

 When tiie key is up the transmitter 

 produces 500 sparks 

 per second, and 

 when it is down, 

 1,000 per second. 

 Thus the signal tone 

 is changed by a full 

 octave, and by 

 mechanically or 

 electrically linking 

 together 25 and i of 

 the signaling keys 

 17 or 23, dots or 

 dashes may be sent 

 at either pitch of 

 spark-note. 



The patent also 

 contains nine other 

 drawings showing details of the spark- 

 gap and stationary electrodes with water 

 cooling (such as is indicated by the 

 pump 45 and circulation system 44), 

 types of oscillation transformers for 

 heavy current, \ariable loading induct- 

 ances, high and low potential relays, 

 etc. -A transmitter in which the alter- 

 nator produces a high \"oltage which may 

 be connected directly across the spark- 

 gap is also illustrated and described. 



A Booth for Long Distance Receiving 



TROUBLE is sometimes experi- 

 enced in recei\ing the faint wireless 

 signals during rainy weather, on account 

 of tlie noi.se caused 1)>- the rain pounding 

 on the roof of the wireless room. 



Tiiis trouble can be o\ercome by 

 building a small double-walled booth, 

 similar to a telephone booth, witiiin the 

 ro(jm in whivh the outfit is placed. Saw- 

 dust should be i)ackeil between the walls 

 and \entilation provitleil \i\ means of 

 two tubi'S, one in the lop and the other 

 near the bottom. 



