Fig. 69. "United Wireless Type Key."
The pivot is a piece of 3/16 inch round steel 1 inch long, and passes through the lever 1 1/2 inches from the rear end. The ends are ground or turned to sharp points and rest in bearings formed by boring a recess in the ends of the thumbscrews. The thumbscrews pass through the center of the bearing, standards 3/4 inch above the base. The lever is clamped to the center of the pivot by means of a small machine screw. A heavy piece of spring brass, S, 1/2 inch wide and 3 inches long, is fastened to the base at one end with a short 8-32 screw. The other end is bent upward so that it presses hard against the lower end of an adjusting screw, which passes through the lever 1 1/4 inches forward of the pivot. This spring serves as an auxiliary conductor and saves the key from carrying an excessive current through its bearings. By adjusting the thumbscrew, the tension of the key may be regulated to suit the operator. The contacts of the key are 1/8-inch round nickel steel alloy or pure silver, set in short 1/4-inch machine screws which fit into correspondingly threaded holes in the base and the lever. This makes the contacts easily removable for renewal. The lower contact is set in a longer screw than the upper one so that connection may be made to it. It is insulated from the base by a hard rubber brushing.
The contacts must be directly above one another and in perfect alignment or else they will pit and stick.
CHAPTER XI. AERIAL SWITCHES AND ANCHOR GAPS.
Some form of switch for quickly connecting the aerial and ground to either the transmitting or receiving apparatus is necessary.
Low powered stations using an induction coil as a transmitter will find a 250-volt double pole, double throw porcelain base switch to be suitable. Such a switch is connected up according to the diagram shown in Fig. 70. As clearly illustrated, the receiving apparatus is in use when the switch is thrown to the right, and the transmitter is ready for operation when the switch is in the left-hand position. The ease and speed with which such a switch may be thrown from right to left or vice versa may be much facilitated by fitting it with a larger and longer handle than the one usually provided.
Fig. 70. Connections for Aerial Switch.
An ordinary double pole, double throw switch should be mounted on the wall within easy reach of the operator, while the two types of switch about to be described are best situated directly on the operating table alongside of the transmitting key.