The helix is raised above the level of the operating bench or table by three small feet fastened to the under head, 120 degrees apart.
Plate III. Transmitting Circuits.
If it is desired to use this helix with the one quarter K.W. transformer, the diameter of the wire should be increased to 5/16 inch. The two K.W. transformer will require seven turns of 1/2-inch hard drawn brass wire two feet in diameter.
Fig. 62. Prague Transmitting Helix.
When setting up a transmitting station, it is a good plan to coil up a long piece of the wire to be used on the helix around a rough form. The adjacent turns should be the same distance apart as they are to be on the finished instrument. Tune up the station with this improvised helix and ascertain the amount of inductance required. It is then easy to design a helix containing the proper amount of wire. Four or five feet extra should be included to allow plenty of range in case it is ever necessary to make any changes in the aerial or condenser.
Fig. 63. Closely Coupled Tuning Circuit.
Plate III illustrates the transmitting circuits of the various commercial systems. The circuit used will determine the number of binding posts and movable clips necessary. Fig. 63 gives the diagram of a very good circuit.