Wireless Telegraph Construction For Amateurs

by Alfred Powell Morgan

Third, the diameter of the core of a wireless coil is generally much larger than that of the ordinary coil, and if a very rapid interrupter is employed there is not time enough to properly magnetize the core before the current is broken.

Fourth, the strength of the losses in the core caused by the eddy currents and hysteresis are proportional to the interruptions in the primary circuit and therefore a low speed will be the most efficient. A rapid interrupter requires a higher voltage and amperage than the same interrupter run at a lower speed.

These are some of the reasons why it is very desirable to use an atomic interrupter or one so adjustable that the rate of the time and duration of the "make" and "break" may be closely regulated. An ideal interrupter is designed to give the longest time possible after contact is established and before the "break" occurs.

It does not pay to construct an interrupter for an induction coil giving sparks up to 2 inches in length. The type of interrupter in use on automobile coils is perfectly well adapted to small coils, and may be purchased complete with the platinum points for as low a price as $1.50.

The mechanical break described below is designed so that various adjustments are possible and it may be adapted to almost any coil. Since it is independent, it need not be mounted directly on the coil, but may be placed in the position most convenient to the operator for adjustment. The interrupter will not operate coils well on an electromotive force above 30 volts, for the excessive voltage causes a spark at the contacts when the circuit is broken and prolongs the decadence of the primary current.

Fig. 34. Independent Interrupter.

Independent Atomic Interrupter.—Fig. 34 illustrates two views of the interrupter. Current is furnished to the electromagnets by a six volt battery independent of the source supplying the coil. The interrupter is set in operation by closing the circuit breaker on the aerial switch. When the primary circuit of the transmitter is then completed by pressing the key, the coil will respond immediately because the interrupter is already in vibration.

The electromagnets (Fig. 35) are a pair of four ohm telegraph sounder magnets. A hole is bored in the center of the top of each magnet core and threaded with an 8-32 tap so that the pole pieces may be fastened thereto, The shape and dimensions of these projections, which must be made of soft iron, are illustrated in Fig. 35.