Detectors are very simple devices and consist merely of an arrangement for holding a small piece of certain minerals and making a contact against the surface.
The crystal detector shown in Figure 210 is a very efficient form that may be easily and quickly made. When finished, it will make a valuable addition to almost any amateur experimenter's wireless equipment.
Fig. 210.—A Crystal Detector.
The bracket is bent out of a piece of strip brass about one-eighth of an inch thick and five-eighths of an inch wide, according to the shape shown in the illustration. The bracket is mounted on a circular wooden base about three inches in diameter. The circular wooden blocks used by electricians in putting up chandeliers, called “fixture blocks,” will make a satisfactory base. An electrose knob of the typewriter type may be purchased from any good dealer in wireless supplies. It should be fitted with a threaded shank which will screw into a hole in the upper part of the bracket.
The mineral is contained in a small brass cup mounted on the base below the end of the knob.
Contact with the mineral in the cup is made by means of a fine wire spring soldered to the end of the adjusting screw.
Moving the screw up or down will vary the pressure of the spring on the mineral and permit the most sensitive adjustment to be secured. The bracket is connected to one of the binding-posts and the cup to the other.
Fig. 211.—Details of the Crystal Detector.