Luxembourg Effect

(or cross modulation), a phenomenon in which, during reception of the radio waves of a radio station operating on a carrier frequency f₁, a broadcast of another strong radio station that is in line with it and is operating on a carrier frequency f₂ that is significantly different from f₃ can be heard. The Luxembourg effect was first observed in 1933 at Eindhoven (Netherlands), where the powerful Radio Luxembourg station, located in line with a Swiss station, could be heard during the Swiss broadcast. A similar phenomenon was observed in the city of Gorky, where powerful Moscow stations could be heard during the reception of radio stations located to the west of Moscow.

The depth of such cross modulation of the radio waves of both stations may reach 10 percent or even more, but it usually does not exceed 1-2 percent. The Luxembourg effect is one source of interference in radio reception. The theory of the Luxembourg effect was developed by the Australian physicists V. Bailey and D. Martyn (1934-37) and the Soviet physicist V. L. Ginzburg (1948).

The cause of the Luxembourg effect is as follows. The absorption of radio waves in the ionosphere is determined by its conductance, which in turn depends on the number of collisions of the electrons present in the ionosphere with molecules and ions. The number of collisions is proportional to the velocity of the electrons, which in the absence of radio waves is determined solely by the temperature of the gas. The mean thermal velocity of electrons v is very great (for example, at room temperature v = 10⁷ cm/sec); therefore, v usually is virtually unchanged, even when radio waves are present in the ionosphere. However, above a strong radio station, where the field intensity of the radio waves is great, the velocity of the electrons—and hence the number of collisions and conductance of the gas—depends on the field intensity (the higher the field intensity, the lower the conductance of the gas) and changes over time in pace with the changes in the field intensity of the powerful station. Radio waves of other stations that pass through the perturbed region of the ionosphere are absorbed first to a greater and then to a lesser extent—that is, they are amplitude-modulated with the frequency of the powerful station. Perturbations produced in the ionosphere by a strong wave affect not only other waves that are propagating in the perturbed region but also the very waves that caused the perturbations. Self-stress of the radio wave in the ionosphere arises. This changes its absorption and phase (that is, it causes distortion of the signal).

Experimental studies of the Luxembourg effect are a method of studying the ionosphere, since they may be used to determine the frequency of electron collisions in the ionosphere and the fraction of energy lost by an electron during a single collision.