On Some Applications of Amplifiers Used in Wireless Telegraphy

(H. Barkhausen, Zwei mit Hilfe der neuen Verstärker entdeckte Erscheinungen, Phys. ZS, 20, p. 401—1919).

At the very beginning of the article the author notes that, when modern amplifiers are used, it is an easy task to amplify a current \(10^4\)-fold. Thanks to this, it becomes possible to perceive alternating electromagnetic fields which previously, because of their weakness, could not be detected. “In the present case,” writes the author, “a kind of microscope with a magnification of \(10^4\) times has been found. Using modern amplifiers, Schottky has shown that one can perceive in a telephone the fields produced in amplifiers by electrons, since the current excited by them exhibits oscillations.

Barkhausen and Tuczeck, using amplifiers, proved that iron makes a sound when it is magnetized. “After a completely” uniform distribution of the magnetic force (before magnetization reversal), writes the author, “the molecular magnets suddenly pass into a new position and excite in a coil placed over the rod disordered induction impulses, which are heard in the telephone as noise.”

As the author showed, the noise is stronger the thicker the iron core being magnetized. For experiments, wire of \(1/3\) or of 1 millimeter is best.

The softer the iron, the weaker the noise. Very soft iron gives such a weak sound that the reversing magnet has to be brought to within \(1/2\) meter. If the magnet is brought almost into contact with the wire, then the sound can be heard in the telephone even without an amplifier. The magnet for reversal is usually turned about its axis by \(180^\circ\).

The second phenomenon described by Barkhausen and of interest for geophysical research is the study of telluric currents, amplified by amplifiers and listened to in a telephone. To obtain these currents, two grounded plates, situated at a distance of 100 meters, are led through an amplifier to a telephone. At certain intervals of time a sound is heard in the telephone which, on the front, was referred to as the sound of a “grenade flight.” The whole phenomenon lasts almost a second. During the war the phenomenon was so strong that a direct wire on the front, listening in on the enemy, became impossible. The phenomena of the currents proceeded in parallel with meteorological phenomena. In May or June it was especially clearly visible on sultry days before noon.

The same sounds are obtained also at sea when copper electrodes are immersed in it. Barkhausen believes that, despite all attempts to explain these earthly currents, they have so far remained unexplained. There is no doubt that the phenomenon described by Barkhausen is of great interest for geophysics.

P. Lazarev.