Interactive simulation of ionospheric cross-modulation —
read the paper
The Luxembourg Effect
In 1933, engineer B.D.H. Tellegen at Philips Research in Eindhoven noticed something strange: while listening to Beromünster (652 kHz, Switzerland), he could faintly hear the program of Radio Luxembourg (230 kHz) superimposed on the signal.
The cause turned out to be ionospheric cross-modulation. Luxembourg's powerful transmitter heated free electrons in the ionosphere's D/E layer, changing how readily they absorbed radio waves. Because Luxembourg's signal was amplitude-modulated, this heating pulsed at audio frequencies — effectively imprinting Luxembourg's audio onto any other signal passing through the same region of ionosphere.
This simulator lets you explore the physics. Adjust transmitter powers, audio tones, and ionospheric conditions to see how the cross-modulation changes. The spectrum plot shows the unwanted Luxembourg sidebands (blue) appearing on Beromünster's carrier, and the transfer function shows how the ionosphere acts as a low-pass filter on the transferred audio.