FIG. 54.—Diagram of aerial switch.
FIG. 55.—Photo of aerial switch.
Spark gaps take other forms, two of which are interesting and important enough to describe here. The first is the rotary gap.
This consists of a number of small electrodes set around the periphery of a wheel mounted upon the shaft of an electric motor. Two other adjustable electrodes are so mounted that the small electrodes on the revolving member pass between. When the motor is set in operation the wheel revolves at a high rate of speed interrupting the spark and causing a peculiar musical pitch to be emitted. A rotary spark gap almost entirely eliminates the arcing of the spark.
The quenched gap consists of a number of disks of brass about five inches in diameter having thin mica washers set between and arranged in a pile as in the illustration. The quenched gap radiates considerably more energy than any other form of gap and also has the advantage of being practically noiseless. The crashing discharge of an ordinary gap produces a very disagreeable penetrating noise hard to eliminate. In most commercial stations the spark is muffled to a certain extent by enclosing it in a cylinder of micanite or some other insulating substance.
FIG. 56.—Anchor gap.
The aerial switch is necessary for quickly connecting the aerial and ground to either the transmitting or receiving apparatus. Amateurs very often employ a small "double pole double throw" switch. The switch used in commercial stations is built in the manner shown in Fig. 55.
