Fig. 203.—Complete Double-Slider Tuning Coil.
When scraping the insulation, be very careful not to loosen the wires or remove the insulation from between them, so that they are liable to short-circuit between adjacent turns.
A Loose Coupler is a much more efficient tuning device than a double-slider tuner, and sooner or later most amateur wireless operators install one in their station.
The loose coupler shown in the figure given on the next page is a very simple one and is both easy and inexpensive to build. Its simplicity is a disadvantage in one respect, however. Owing to its construction, it is impossible to move the slider on the secondary when the latter is inside the primary. The reason that I have chosen this sort of loose coupler to describe is to acquaint my young readers with the methods of making a loose coupler.
The "Junior" loose coupler described farther on is a more elaborate instrument of greater efficiency, but much harder to build.
Fig. 204.—A Simple Loose Coupler.
The base of the loose coupler is of wood and measures twelve by four inches. The head supporting the primary is of the same size as those used on the "Junior" double-slide tuning coil just described. It may be made in the same manner, and fitted with a circular block to support the tube. The primary tube is of the same diameter as that on the tuning coil but is only four inches long. It is fastened to the primary head with glue and then secured with a number of small tacks. One or two coats of shellac liberally applied will render it non-shrinkable, so that the wire will not be apt to loosen after the loose coupler has been in use a while.
The secondary is of the same length as the primary, but of smaller diameter, so that it will easily slip inside. It also is treated with shellac.