The night the ionosphere stopped being a mirror
2026-03-05 · EA5IYR
In 1933 an engineer in Eindhoven named Bernard Tellegen was listening to a Swiss station on 652 kHz when he noticed something underneath it.
Faint, but unmistakable: the programme of Radio Luxembourg, which was not on 652 kHz and was several hundred kilometres away in a different direction.
He was not the only one. A listener in Portsmouth had reported hearing Radio Paris underneath Radio Luxembourg the same year. Why this was a problem
Not a practical problem. A conceptual one.
The ionosphere was understood to be a passive mirror. Signals went up, bounced, came down, and were otherwise unaffected. Two signals passing through the same region did not interact, any more than two torch beams crossing in a room interact.
Hearing one station's audio riding on another's carrier meant that assumption was wrong. What is actually happening
Radio Luxembourg was extremely powerful. Where its beam passed through the ionosphere it did something measurable: it accelerated the free electrons there, which changed how often they collided with other particles, which changed how much energy that patch of plasma absorbed.
And it did all that in time with its own programme, because the transmitter's power rose and fell with the audio.
So a second, weaker signal crossing the same patch was absorbed slightly more during Luxembourg's loud passages and slightly less during its quiet ones. By the time it reached a receiver it was carrying a faint copy of a programme it had never been anywhere near.
Bailey and Martyn published the theory in 1934. It has been called the Luxembourg effect ever since, after a broadcaster that had nothing to do with discovering it. What it led to
Everything. This is the observation that established the ionosphere as a non-linear medium — something you can push on and get a response from, rather than a fixed mirror overhead.
Once you accept that a transmitter can modify the ionosphere, you can start doing it deliberately, and the entire field of ionospheric modification follows. The heating facilities that exist today in Alaska, Norway and Russia are the industrial descendants of a Dutch engineer noticing a second programme where there should have been silence. Can you still hear it?
Rarely, and it needs the conditions: a very strong transmitter, a weaker one crossing its path in the ionosphere, and you positioned to receive the second. The great era of enormous long-wave and medium-wave transmitters is largely over, and with it most of the opportunities.
It has been observed and measured in the modern era, including deliberately using heating facilities. But the original way of encountering it — sitting at a receiver at night and noticing that something is wrong — is much harder to come by now.
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Sources: SWLing Post — the Luxembourg-Gorky effect explained, PA3FWM — sideband asymmetry in the Luxembourg effect, Radio Science — sideband asymmetry in ionospheric cross modulation, OneTubeRadio — the Luxembourg effect.