Tech UPTechnologyWho sent the mysterious radio signal that was received...

Who sent the mysterious radio signal that was received in Oslo in 1927?


PCJJ was the first shortwave radio station in Europe and the first in the world dedicated exclusively to that part of the electromagnetic spectrum. Installed by Philips in the Dutch city of Eindhoven, it began broadcasting on March 11, 1927 with a broadcast to the Dutch East Indies with the words “Hello Dutch East Indies, this is a broadcast from Philips Laboratories in Eindhoven.” PCJJ soon started broadcasting in English, Spanish, German and Dutch all over the world.

But what this station has gone down in the history of mysteries for is not because of Queen Wilhelmina’s speeches on different colonial issues on May 30 and June 1 of that year, but because of something stranger that happened at the end of the summer of 1927.

According to what the physicist from the University of Oslo Carl Størmer (the first scientist who measured the height at which the northern lights occur) told Nature magazine, on February 29, 1928 he received a letter from the engineer Jørgen Hals, who was in what is now called Bygdøy, a neighborhood in Oslo, where he said: “I hereby have the honor to inform you that in the late summer of 1927 I repeatedly heard short-wave signals from the transmitting station PCJJ (Eindhoven). At the same time that I heard the signals, I also heard echoes. I heard the usual echo when the signal goes around the Earth 1/7 of a second later, but also a weaker echo 3 seconds after the main signal. Where it came from I can’t say anything; I can only confirm that I heard it .”

The Dutch physicist and expert in the propagation of radio waves Balthazar Van der Pol was intrigued and decided to help Størmer and Hals, who were looking for an explanation. They busily tried to find a way to reproduce this result. For two years his experiments included test transmissions from the Netherlands and occasionally Indonesia in what has probably been the largest effort ever to study this elusive new phenomenon, long-delay radio echoes. After several attempts, on October 11, 1928 they succeeded. A telegram from Størmer saying that he had clearly received a series of echoes that afternoon put Van der Pol on notice: “I decided to send that same night a series of test signals consisting of 3 Morse points in rapid succession every 30 seconds, between 8:21 p.m. local time.

a key experiment

But the most spectacular result was obtained on October 24, 1928: simultaneous observations in Norway and the Netherlands of the echoes of the PCJJ signals at a wavelength of 31.4 meters (9.55 Mhz). Echoes of the agreed signal -three Morse points in rapid succession every 30 seconds- were received both in Oslo and in two stations in Eindhoven. Van der Pol received 9 echoes in the Netherlands , delayed from their respective signals by between 3 and 30 seconds; in Oslo, 20 echoes. They were also heard in the UK by a group led by Edward Victor Appleton (a physicist who would receive the Nobel Prize in 1947 for his studies of the ionosphere). These results convinced most skeptics at the time that the effect was real, and probably still remain the most convincing evidence that such long-delay radio echoes exist .

Something similar happened on July 7, 1974 when HL Rasmussen studied the reflection of radio waves on the surface of the Moon. The methodology was very simple: send a series of signals to our satellite and wait 2.6 seconds to receive them reflected. “Suddenly a second signal appeared delayed about 2 seconds. It had the same characteristics as the reflected one, only it was weaker.” The phantom signal appeared on different occasions that day, a few seconds after receiving the one reflected by the Moon. Rasmussen postulated in the journal Nature that it could be a second reflection in a solar plasma jet, but they still remain unexplained .

What was the origin of those echoes? In 1989 AG Shlionskiy published in the journal Telecommunications and Radio Engineering up to 15 possible causes that can be essentially grouped into two groups: either the signals are reflected from outer space – for example from the Moon or from small interplanetary gas clouds near the Earth – Or they come from areas of the atmosphere linked to our planet, such as the magnetosphere.

A message from an alien civilization?

Far more fascinating was the explanation offered by Ronald Bracewell, a professor of electrical engineering at Standford University, writing in 1960 in the journal Nature: They could be the way an advanced galactic society communicated with us with an unidentified space probe. manned in the surroundings : “To be sure that a radio signal can penetrate our ionosphere and is in a band that we are using, the probe would first listen to our signals and repeat them. To us, their signals would have the appearance of echoes with delays of seconds or minutes , like those reported thirty years ago by Størmer and van der Pol and never explained.” Half jokingly, half seriously, in 1972 the British astronomer Duncan Lunan set out to see if Bracewell could be right. And he found that the delays recorded by Van der Pol on October 11, 1928 were actually points on a map. If a graph was made where the delay in seconds of each echo was represented against the order in which they were received, an incomplete image appeared, but recognizable by any astronomer: the constellation of the Boyero.


Crawford, FW; Sears, DM; Bruce, RL (1970) “Possible observations and mechanism of very long delayed radio echoes,” Journal of Geophysical Research, Space Physics, vol. 75, no. 34, p. 7326–7332

Bracewell, R.N. (1960). “Communications from Superior Galactic Communities”. Nature. 186 (4726): 670–671. doi:10.1038/186670a0

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