Are We Alone? Listening for Signals in an Increasingly Noisy Radio Sky

The search for extraterrestrial intelligence may sound a long way removed from amateur radio, but an excellent new article from the International Telecommunication Union (ITU) shows that radio astronomers and amateur weak-signal operators increasingly share the same problem: finding extraordinarily weak signals in an increasingly noisy radio environment. Written by Boris Sorokin, Radio Spectrum Engineer with the SKA Observatory, the article explores how SETI researchers search for artificial signals from distant star systems and why protecting a quiet radio spectrum is becoming critical to that work. Modern projects such as Breakthrough Listen are already examining millions of stars and billions of radio channels, while the developing Square Kilometre Array (SKA), including SKA-Low in Western Australia, will dramatically increase our ability to search the Milky Way for signals that cannot be explained by natural processes.

The challenge has a fascinating parallel with amateur radio astronomy, EME, weak-signal VHF/UHF and microwave operation. The signals being sought by SETI can be many orders of magnitude weaker than everyday terrestrial transmissions. Radio amateurs attempting to detect extremely weak signals know precisely what happens when the noise floor rises or an unwanted carrier appears in the passband. The difference is that radio astronomers may be listening for a signal that has travelled thousands of light-years, while amateurs might be trying to recover an EME signal that has merely made the 768,000-kilometre round trip to the Moon. In both cases, receiver sensitivity, antennas, signal processing and, crucially, a quiet spectrum determine whether the signal is detectable.

There is, however, a particularly interesting twist to the interference problem: the source may no longer be terrestrial. Tens of thousands of satellites already orbit Earth, with potentially hundreds of thousands more proposed. Apart from their intended transmissions, satellites can generate unintended electromagnetic radiation from onboard electronics. For SETI researchers this creates a double problem. These signals can overwhelm genuine astronomical emissions, while an artificial-looking signal from Earth orbit must also be eliminated before researchers can consider the rather more exciting possibility that it came from somewhere beyond Earth. In 2019, for example, a narrowband signal apparently arriving from the direction of Proxima Centauri generated considerable interest before almost a year of analysis concluded that the BLC-1 candidate was terrestrial interference.

This should sound remarkably familiar to amateur experimenters. Interference hunting has traditionally involved looking for switch-mode power supplies, solar inverters, LED lighting, computers and other sources somewhere around the neighbourhood. Increasingly, however, not every unwanted signal need originate somewhere down the street. Satellite constellations introduce intentional, unwanted and unintended RF emissions into the radio environment from above. For amateur radio astronomy and weak-signal experimentation, distinguishing a genuine astronomical or propagation phenomenon from human-made RF is becoming an increasingly sophisticated exercise.

The issue is significant enough to feature in preparations for the ITU World Radiocommunication Conference 2027 (WRC-27). Agenda items include protecting radio quiet zones and radio astronomy bands from aggregate interference produced by large non-geostationary satellite constellations, examining direct satellite-to-phone services, considering communications around the Moon and protecting radio astronomy above 76 GHz from unwanted emissions. These international spectrum discussions have obvious parallels for amateur radio: once the electromagnetic environment becomes sufficiently noisy, even the best receiver cannot recover a signal buried beneath interference.

For Australian amateurs interested in radio astronomy, SDR, EME, satellite operation, microwave experimentation or weak-signal communications, the ITU article is particularly worthwhile reading. It also provides another reminder of why spectrum management, electromagnetic compatibility and control of unwanted emissions matter to all radio services.

Full credit to Boris Sorokin, the SKA Observatory and the International Telecommunication Union for the original article.

Image sourced from the article.

Read the full ITU article: Are we alone? Listening for neighbours in an ever-noisier sky - Link

Page Last Updated: Thursday, 20 Aug 2026 at 20:55 hours by Justin Giles-clark

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