A Noisier Radio Sky: Satellite Interference Challenges Radio Astronomy

The International Telecommunication Union (ITU) has highlighted a growing challenge for radio astronomy: the rapid expansion of large satellite constellations and the many different radio signals they can produce. In an article published on 14 August, Australian radio astronomer and spectrum manager Balthasar Indermuehle of CSIRO, together with Federico Di Vruno of the SKA Observatory, explain that astronomers are now detecting thousands of satellite signals, including some within bands protected for radio astronomy. Observations have been made using facilities including LOFAR in Europe, the SKA-Low prototype in Western Australia, the South Pole Telescope, and the Mopra and Australia Telescope Compact Array facilities in New South Wales.

The authors identify three distinctly different interference challenges. Intended emissions are the signals satellites are designed to transmit, such as broadband internet, satellite telephone, broadcasting and direct-to-cell services. Unwanted emissions include out-of-band energy and spurious signals such as harmonics produced by transmitters. The third category, unintended radiation, is particularly interesting: RF energy generated not by the communications transmitter itself but by electronics elsewhere in the spacecraft, including switch-mode power supplies, clocks, oscillators, digital systems, motor controllers and solar-panel inverters. Measurements of second-generation Starlink satellites, for example, have detected broad and narrowband radiation between 110 and 188 MHz at levels capable of potentially interfering with radio astronomy operations.

There are some striking parallels here for amateur radio. Anyone who has hunted interference around the shack or neighbourhood will recognise the suspects: switch-mode supplies, digital electronics, oscillators, inverters and control systems. The difference is that astronomers are trying to detect some of the faintest radio signals reaching Earth, while the unwanted source may now be travelling overhead in low Earth orbit. The underlying lesson is familiar to amateurs: a device does not need to be deliberately transmitting on your frequency to cause interference. Harmonics, out-of-band emissions and unintended radiation can all raise the noise floor or mask weak signals. For amateurs interested in weak-signal VHF/UHF, EME, satellites, microwave operation and radio astronomy, the issue has particularly obvious parallels.

The issue is also becoming an important part of international spectrum management ahead of WRC-27. Existing ITU Radio Regulations already address unwanted satellite emissions, but the authors argue these requirements need to be applied as rigorously as they are to terrestrial transmitters. Unintended spacecraft radiation presents a newer regulatory challenge, and work is now underway between ITU-R, CISPR and ISO on practical electromagnetic compatibility limits for spacecraft.

This message is one radio amateurs understand rather well: as our electromagnetic environment becomes more crowded, controlling unwanted RF emissions becomes increasingly important if weak-signal services are to remain usable.

Full credit to Balthasar Indermuehle, Federico Di Vruno and the International Telecommunication Union for the original article.

Read the full ITU article:
Three kinds of satellite signal, three challenges for radio astronomy - Link

Image sourced from the ITU article.

Page Last Updated: Tuesday, 18 Aug 2026 at 21:29 hours by Justin Giles-clark

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