Spark Transmitter

At the end of his scientific research carried out in 1887/1888 Heinrich Hertz was able to prove the existence of electromagnetic waves and describe some of their characteristics. The experiments were not only a scientific sensation, but also enabled Guglielmo Marconi, the first ‘radio dabbler’ to set up a communications path for morse traffic. In 1896, Marconi successfully covered a distance of about 3 km using electromagnetic waves. A little later, he established radio contact across water between Lavernock Point, South Wales and Flat Holm Island. The transmitter consisted of a spark inductor coupled to a dipole antenna. At the receiver side, he used another dipole and a glass tube filled with silver and nickel filings, the so-called coherer. The filings enabled the coherer to act as a ‘defined’ bad contact with the RF pulse energy ‘rattling’ the contact and thus driving the audio amplifiers connected to the output.
The circuit shown here operates on the same principle.