Electrolytic detector

The radio transmitters of the time transmitted information by radiotelegraphy; the transmitter was turned on and off by the operator using a switch called a telegraph key producing pulses of radio waves, to transmit text data using Morse code.

In the process of stripping some Wollaston wire, Fessenden left it immersed in acid too long, eating away most of the wire until only a tip remained in contact with the solution; he noted that it responded well to radio signals being generated nearby, and could be used as new type of detector.

This story was disputed at the time, with credit for the discovery also given to Michael I. Pupin, W. Schloemilch, Hugo Gernsback and others.

The action of this detector is based upon the fact that only the tip of a platinum wire a few hundred-thousandths of an inch in diameter is immersed in an electrolyte solution, and a small D.C. voltage bias is applied to the cell thus formed.

The wire is made positive, and the signal to be demodulated is applied directly to it; a small (about 5 ml) platinum cup filled with either sulfuric or nitric acid completes the headphone circuit, and is also connected to ground to complete the signal circuit.

The potentiometer setting is then moved to reduce the current until the noise just ceases, at which point the detector is in its most sensitive state.

The operation was the same as in the bare-point electrolytic detector, the advantage being that the acid was sealed in, and consequently could not spill or evaporate.