High Frequency Apparatus Page 58

58 HIGH FREQUENCY APPARATUS The primary is composed of twelve turns of very heavy copper wire such as is used for the transmitting helix in a wireless set. The wire is wound upon dowel rods set up in the base surrounding the secondary coil. The rods should be so placed that the inside diameter of the primary winding is 1½ times the diameter of the secondary. The winding of heavy wire should cover 2/3 of the height of the secondary cylinder. If the induction coil used to excite this oscillation transformer is of large size, the secondary may send sparks into the primary. In this case, the primary must be made larger in diameter. The directions here have been for a comparatively close-coupled coil as that type will give maximum results with the usual wireless spark coil. The lowest turn of the primary helix is to be connected with the ground terminal to which the lower end of the secondary winding is attached. The wiring diagram is given in Fig. 4, and the reader will notice that the spark gap is connected across the secondary of the spark coil; the condenser and primary of the resonator are in series across This und fast on spindle Thread Wire Wind thread and wire in parallel. Remove thread when winding is complete. This end free on center Fig. 2. Apparatus for winding secondary of oscillation transformer