Page:Popular Science Monthly Volume 91.djvu/469

 Popular Science Monthly

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��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.

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