The carborundum detector is a form of crystal rectifier consisting of a fragment of carborundum held between two carbon blocks.
The electrolytic detector consists of a very fine platinum wire (.001-.0003 of an inch in diameter) dipping into a small cup of dilute nitric acid. A large platinum electrode is sealed in the bottom of the cup so as to make an electrical connection with the liquid. This form of detector is exceedingly sensitive, probably more so than any other. The electrolytic detector requires a battery. When a slight current passes through the circuit, very minute bubbles are formed at the wire, insulating it from the liquid and thus shutting off the battery current from the telephone receivers. However, upon the arrival of any electric waves and consequent high frequency oscillations the latter destroy the bubbles clustering around the little wire and permit the current to flow. Upon the cessation of the high frequency currents the bubbles immediately form again, only to become broken down by each train of oscillations produced in the aerial. The intermittent currents can be detected by a buzz in the telephone receivers.
FIG. 73.—Electrolytic detector in circuit.
The carborundum detector also requires a battery although its action is somewhat different from that just described.
FIG. 74.—Potentiometer.
When a battery is used in connection with a detector, an instrument known as a potentiometer becomes necessary. A potentiometer is simply a device for accurately adjusting the voltage of a battery to a value where it will render the detector the most responsive to the incoming signals.
FIG. 75.—Diagram showing how potentiometer is connected in circuit.