Popular Science Monthly 



299 



and the condensers D6 so that the sound 

 of the dots is somewhat different from 

 that of the dashes. This gives in effect 

 a two-tone system, and obviously per- 

 mits higher signaHng speeds than does 

 the usual dot-and-dash method. In ad- 

 dition to the increase in speed the two- 

 wave lengths feature oft'ers excellent se- 

 curity from interception of the messages 

 by ordinary radio receiving stations. 



When the signals 

 received are sutti- 

 ciently strong to 

 operate a sensitive 

 relay it is possible 

 by this method to 

 make a siphon re- 

 corder pen-and-ink 

 record correspond- 

 ing exactly to cable 

 "slip." If a relay is 

 connected to each 

 side of the receiv- 

 ing system, the two 

 contacts may be 

 used to control a 

 third polarized re- 

 lay which will re- 

 main in an open 

 neutral position so long as no signals are 

 received, but which, when waves are ar- 

 riving, will close its local circuit and per- 

 mit current to flow in one direction or 

 the other according to whether it is 

 operated by a dot-impulse or a dash- 

 impulse. A siphon recorder in this last- 

 named local circuit will recoid the sig- 

 nals by a wavy line having a hump above 

 its neutral position along a central line 

 for each dot, and a hump below for each 

 dash. Fig. 3 shows the actual connec- 

 tions of apparatus set up to accomplish 

 this result, and in this diagram the action 

 may easily be traced from the sensitive 

 relays U U, which are connected to the 

 two detectors, to the siphon recorder g. 



U. S. Patent No. 1127921, issued to 

 G. W. Pickard, is on an important detail 

 of receiving tuning apparatus. Before 

 the adoption of inductance varying ar- 

 rangements similar to that shown in this 

 specification it had been customary to 

 rely upon either sliding contacts, vario- 

 meters or roller inductances for tuning. 

 Each of these methods has disadvan- 

 tages; sliders give poor contact at times. 



Fig. 3. Relay connections for recorder operation 



and cause loss of energy through short- 

 circuited turns; variometers are limited 

 in range of adjustment, and have their 

 total resistance in circuit even at mini- 

 mum inductance ; roller arrangements 

 are bulky, and slow in operation. All 

 these difficulties may be overcome by the 

 use of multiple-point switches connected 

 to the turns of the coils, but it would be 

 practically impossible to have a switch- 

 point for each sin- 

 gle turn of a long 

 coil. If a saving in 

 the size of the 

 switch is attempt- 

 ed, by making each 

 point cover a num- 

 ber of turns, it is 

 not found possible 

 to get sharp enough 

 tuning unless a n 

 auxiliary variable 

 inductance or con- 

 denser is used. 



The plan of 

 wiring shown in 

 Fig. 4 makes it 

 possible to get sin- 

 gle-turn steps of 

 inductance on a long coil by using two 

 small switches. One of these, indicated 

 l)y S, has taps taken off the body of the 

 coil at each tenth turn. The other. Si, 

 has its points connected to each of the 

 last ten single turns on the coil. The 

 leads to the coil, A and G, run to the 

 levers of the two switches ; and each ter- 

 minal may be connected directly to the 

 tenth turn of the coil by placing its re- 

 spective switch lever on a button marked 

 "O." This common zero of the two 

 switches seems to be the novel point in 



Fig. 4. 



Common zero 

 inductance coil 



switches on 



the present patent, and is the artifice by 

 which it is possible to adjust to any in- 

 ductance from zero to full value by steps 



