Sparks as radioemitters

Abstract

In the early experiments on radiocommunication, Hertz, Branly, Lodge, Marconi used as emitter a spark produced by a high electric tension. Why did this spark emit an electromagnetic radiation? The phenomenon is well understood in the case of the device used by Hertz in 1887. It is not so clear in the device used by Branly in 1890. Hertz used a set of two big metallic spheres (or other big objects) as a capacitor whose discharge produced a spark in a burster. It is argued that in Branly’s device the spheres of the burster are also a rather efficient capacitor. The main differences with Hertz’s device are: (i) the frequency spectrum is much broader and higher; (ii) the capacity is about ten time smaller; (iii) a quantitative analysis, if feasible, would be very difficult.

Keywords

• Electromagnetism
• Radiocommunication
• Discharge
• Self induction
• Hertzian waves