Popular Science Monthly 



453 



reversed also, that is A the flux in core N is 

 diminished and an electromotive force is 

 induced in the secondary windings S, while 

 the flux in core N' remains practically the 

 same and no E. M. F. is induced in the 

 winding S' . Due now to the manner in 

 which the secondaries are connected to- 

 gether, the last induced E. M. F. produces a 

 current through the secondary circuit in the 

 same direction as that produced by the 

 first E. M. F., giving the current represented 

 by G H. As this is repeated over and over 

 again, many times in a second, the second- 

 ary current obtained goes through twice 

 as many cycles as the initial current and 

 it is therefore of twice the frequency of 

 the initial current. 



The new current is now led into an 

 exactly similar transformer and its fre- 

 quency is again doubled, giving a current 

 which is now of a frequency four times 

 that of the initial current. In the Arco- 

 Joly system as used at Sayville, Long 

 Island, the generator supplied a frequency 

 of about 8,000 cycles per second, so that 

 the frequency of the current supplied to 

 the antenna was 32 ,000, which corresponded 

 to a 9,400 meter wavelength. The electrical 

 and magnetic losses were kept down by 

 making the cores of very thin iron sheets, 

 which were insulated from each other, and 

 by making the windings and connecting 

 wires of separate strands, some 2,000 in 

 number, two-hundredths of a millimeter in 

 diameter, and each one insulated from the 

 other. The power sent through the coils 

 amounted to over a hundred horsepower, 

 so that to keep them from burning up they 

 were immersed in tanks of circulating oil. 

 The generator itself was water cooled. 



Loading Coil in Series with the 

 Secondary 



WHEN a low resistance detector is 

 used, it is a good plan to tune the 

 secondary circuit by using a comparatively 

 small inductance coil and a large condenser, 

 for then the current flow is at maximum and 

 the voltage is quite low. For high resist- 

 ance detectors the reverse is true. In- 

 creased efficiency with such detectors as the 

 audion can frequently be secured by 

 inserting a loading coil in series with the 

 secondary, and correspondingly reducing 

 the capacity of the tuning condenser. 

 This applies the highest possible voltage to 

 the grid. 



Double Set of Receivers to 

 Amuse Visitors 



THE amateur who is continually having 

 visitors will find two sets of binding 

 posts for the telephones very handy. 

 These can be best placed one pair at each 



TWO POINT 

 SWITCH 



TO RECEIVER 

 Two pairs of binding posts on each side 

 of the receiving set for an extra telephone 



side of the receiving set. A two-point 

 wood base switch, connected as shown in 

 the illustration, will short-circuit either 

 pair of telephones or leave both in cir- 

 cuit. — Harry N. Bliss. 



A High Voltage Lead-In 

 Insulator Tube 



THE leading-in insulator described is 

 cheap and effective, and will withstand 

 the voltage of an ordinary 2 kw. trans- 

 mitter. It is made from a hard rubber or 

 composition telephone-receiver shell and 

 two water-gage tubes. 



A 2 by 34-in. brass bolt is run through 

 the cord-hole in the receiver-shell, after 

 having soldered to its head some twenty 

 strands of No. 20 or 22 copper wire, long 

 enough to reach through the gage-glasses. 

 The tubes are placed one over the other and 



A brass bolt 



Sealing wax 



Two water glass gages carrying a high 

 voltage lead-in wire run through a wall 



the wires run through; then the glasses 

 are cast into the receiver-shell with sealing 

 wax. A hole is drilled through the wall and 

 the tubes slipped through and fastened with 

 friction-tape. The water glass tubes are 

 long enough to receive the rubber part of a 

 telephone receiver on the inside for ap- 

 pearance. — D. R. Simmons. 



