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.
[Illustration: 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.
All insulated parts of an aerial switch such as the base, insulating bar, handle, etc., should be made of some good insulating material, as porcelain, hard rubber or ebonite. All insulation which is used in power switches such as slate, wood, marble, etc., is worthless and should not be used.
If a loop aerial system is used, a switch is necessary, which will break the primary transmitting current so that in case of an accidental touch of the key while receiving, the high voltage discharge will not pass across the anchor gap into the receptor and badly damage the same or shock the operator. The connections of such a switch and the loop aerial are shown in the wiring diagram of the De Forest system.
[Illustration: Fig. 71. Aerial Switches.]
A switch may be easily constructed from a 50 ampere, single throw, triple pole, fuseless power switch. If it is mounted on a slate base remove it and set it up on a base of the same size made of fiber or porcelain. Flat unglazed tiles of various sizes are obtainable from tile setters at a very low cost. They may be easily bored with an ordinary steel twist drill. Such tiles are excellent insulators when not exposed to moisture and are useful for bases, etc., in many cases. A heavy coat of shellac varnish will make the tile impervious to moisture.