452 



Popular Science Monthly 



Alternating current is supplied by the 

 generator G to the stator S of the Gold- 

 schmidt alternator through the choke-coils 

 A and the interrupting key K, as shown 

 in Fig. 2. As the alternator is revolved 

 by an auxiliary motor, the current set up 

 in the rotor R is made very large by 

 connecting the circuit DEF to the rotor 

 so that the impedance, that is, the apparent 

 resistance, to the current is made very 

 small and the current made correspondingly 



One of the two frequency-doubling trans- 

 formers of the Arco-Joly sending system 



large. The current is then reflected back 

 into the stator as explained before, and 

 the new current of double the original fre- 

 quency is also provided with the tuned 

 electrical path CL so that the impedance 

 for it is also very small. Reflecting the 

 current again into the rotor gives an- 

 other current of three times the original 

 frequency. This too is provided with a 

 circuit of very small impedance, which 

 allows the current to become comparatively 

 large. The last reflection takes place from 

 the rotor to the stator and it is this current 

 that was used in the antenna. To accom- 

 plish this, the antenna was connected to / 

 and the ground was connected to /, as 

 shown in the diagram; the loading coil B 

 and the condenser C having been adjusted 

 until the antenna was tuned to agree with 

 the last reflected frequency. 



In this manner, currents which have the 

 high frequency of 60,000 — or 60,000 cycles 

 of changes in direction per second — were 

 readily obtained. The alternator was 

 driven at a speed of nearly 10,000 revolu- 

 tions per minute. The best results were 

 found to be obtained on reflecting the cur- 

 rents four successive times. Theoretically, 

 there is no limit to the number of times they 

 may be reflected, but practically on reflect- 

 ing them more than four times, the electrical 

 and magnetic losses become excessive. 



The Arco-Joly system uses a number of 

 separate transformers so constructed that 

 the frequency of the initial current is 

 doubled every time it goes through a 

 transformer. The construction of the 

 separate transformers is as shown in Fig. 3. 

 The transformer has two independent cores 

 and an auxiliary circuit K, K' supplying 

 a direct current, which is sufficiently large 

 nearly to saturate both of them magnetical- 

 ly. The initial current is supplied to the 

 primaries P and P' of the transformers by 

 the alternator G and the curve represent- 

 ing its strength is an ordinary sine curve 

 as shown by A BCD in Fig. 4. The 

 capacity C and the inductance L are 

 made of such values that the impedance 

 of the circuit CLPP is very small. This 

 causes the current in that circuit to become 

 correspondingly large. On account of the 

 manner in which the auxiliary winding K 

 is connected, as the initial current passes 

 through the stage shown by AB in Fig. 4, 

 the increased magnetization of core N 

 amounts to practically nothing. This is 

 because the core is already saturated by 

 the auxiliary direct current and also because 

 the winding of P is such as to make it tend 

 to add to the already saturated flux. In 

 N', however, due to the fact that winding 

 K' is in the reversed direction to that of K 

 the current in P' tends to decrease the 

 total flux in the core N'. This can readily 

 be done, and as the flux diminishes in 

 strength, the change 

 in flux induces an 

 electromotive force in 



Curve showing how the first transformer ■ 

 makes the original current uni-directional 



the secondary winding S'. The result is 

 the secondary current roughly represented 

 by EF in Fig. 4. As the initial current 

 reverses in direction, as shown by CD in the 

 same illustration, it is evident that the 

 phenomena in the core N- and N' are 



