The rotary gap, commonly used by amateur experimenters and consisting of a toothed disk mounted on the shaft of a small motor is of the non-synchronous type.
Rotary gaps are sometimes enclosed in an air tight case and the electrodes arranged so that the results obtained are characteristic of both the quenched and rotary gaps. This type of gap is known as the rotary quenched.
LESSON NINETEEN. THE KEY.
Some means of controlling the currents flowing through the transmitter in order to divide them into periods corresponding to the dots and dashes of the Morse Code is necessary.
This is supplied by a hand operated switch, called a key. A key used for wireless purposes must be much larger and heavier than an ordinary key employed for line work in order to carry the more powerful currents.
In spite of the size and weight of a wireless key, if it is properly balanced, it may be handled with perfect control and ease.
The contact points of a wireless key are necessarily large and heavy. Special alloys found to be the most suitable for the purpose are usually employed. A large condenser having a mica dielectric is very often connected across the contacts to reduce the sparkling.
FIG. 42. Wireless Key.
In very large stations where extremely heavy currents must be handled, the key controls a large switch operating in oil. Every time the key is pressed the switch closes and when the key is released, opens. The currents of the transmitter are "made" and broken by the switch without passing through the key.