Exploring Ambient Radio Frequency Emissions

Radio astronomy observatories, such as the Dominion Radio Astrophysical Observatory in Penticton, British Columbia, try to limit radio frequency interference to observe incredibly faint astronomical signals. These protective measures include placing observatories in geographically remote locations, the implementation of radio-frequency-interference-free quiet zones, or removal of interference in data processing. In 2018, we set out to explore how necessary radio-quiet zones are, by studying the radio frequency emission around the Observatory and around our local environment in Calgary, Alberta. We studied five well-used radio frequency bands and found the emission to be variable and environment dependent. While the radio frequency environment has changed since then, as a consequence of increased satellite activity and other forms of emission, we present these results as documentation of the past environment with the aim to redo the measurements. Overall, as there is use from both public and private services across the radio spectrum, protective measures at astronomical observatories are essential to reduce radio frequency interference.

💡 Research Summary

The paper presents an empirical investigation of the radio‑frequency (RF) environment surrounding a major radio‑astronomy facility (the Dominion Radio Astrophysical Observatory, DRAO, near Penticton, British Columbia) and a representative urban area (Calgary, Alberta). Conducted in 2018, the study measured ambient emissions in five frequency bands that are heavily used by modern communications: two cellular bands (824‑960 MHz and 1710‑2170 MHz), the industrial‑science‑medical (ISM) band (2400‑2500 MHz), the traditional radio‑astronomy allocations (406‑410 MHz and 1405‑1435 MHz), and a broader “radio‑communication” band that includes legacy services.

Measurements were taken at twelve distinct sites that span a wide range of environments: four indoor locations on the University of Calgary campus (a student hub, a technologically advanced institute building, a semi‑isolated laboratory, and a “Quad” area between two administration buildings), three outdoor urban sites (a large park, an apartment complex, and a street‑level location in a busy neighbourhood), three rural sites outside the city (a highway rest area, the front and back slopes of Mount Yamnuska), and two sites at the DRAO itself (inside the designated radio‑quiet zone and just outside it). Each site was scanned with a Keysight N9343B spectrum analyzer covering 100 kHz‑3 GHz with a resolution bandwidth of 10‑100 kHz. The campaign comprised two measurement windows (March–June 2018), with each location sampled for roughly two minutes per scan and the average power recorded for each band.

The results reveal a clear spatial dependence of RF interference. In the dense urban locations, the cellular bands dominate: average power levels range from –70 dBm to –90 dBm, with the Quad and the student hub showing the strongest persistent signals (≈ –85 dBm). The ISM band also exhibits substantial activity, reflecting ubiquitous Wi‑Fi and Bluetooth devices. By contrast, the rural sites and the DRAO interior display markedly lower levels. In the dedicated radio‑astronomy bands, most measurements are below –100 dBm, indicating that the quiet‑zone concept is largely effective. However, a notable exception is a –85 dBm spike at 409.9 MHz recorded just inside the DRAO quiet zone, which the authors attribute to leakage from a nearby cellular transmitter. The 1405‑1435 MHz band, reserved for scientific use, shows virtually no detectable emissions in any location, confirming its relative protection.

The authors interpret these findings as evidence that radio‑quiet zones provide a tangible reduction in RFI for sensitive astronomical observations, but they also highlight that complete isolation is unrealistic without additional shielding and active monitoring. They point out that even within the quiet zone, strong out‑of‑band emissions can intrude, especially when the surrounding environment is densely populated with transmitters.

Methodologically, the paper has several strengths: the use of a broadband, high‑resolution spectrum analyzer enables detection of weak signals; the selection of a diverse set of measurement sites captures spatial variability; and the focus on both public (cellular, ISM) and scientific (radio‑astronomy) allocations provides a holistic view of the spectrum usage. Nonetheless, the study has notable limitations. Temporal resolution is coarse—measurements were taken only twice over a four‑month period, precluding analysis of diurnal traffic peaks, weekend versus weekday patterns, or seasonal changes. The analysis relies primarily on average power; it does not present peak‑to‑average ratios, duty cycles, or spectral density metrics that would better characterize intermittent or bursty interference. The noise floor of the instrument was adjusted by only 1 dB, which may obscure very weak astronomical signals near the detection limit. Finally, the work does not incorporate the rapidly growing satellite‑based RFI (e.g., Starlink, OneWeb) that has become a dominant source of interference since 2018.

In the discussion, the authors call for continuous, long‑term monitoring using low‑cost software‑defined radio (SDR) platforms, integration of real‑time RFI databases with regulatory bodies (ITU, national spectrum agencies), and the development of adaptive mitigation techniques (e.g., dynamic frequency excision, beamforming nulls). They also suggest that future studies should expand the statistical treatment of the data, include higher‑resolution time‑frequency analysis, and assess the efficacy of physical shielding measures (e.g., Faraday cages, underground cabling) in conjunction with policy‑level protections.

Overall, the paper documents a valuable snapshot of the RF environment in 2018, confirming that urban RF congestion is substantial and that radio‑quiet zones remain essential for preserving the integrity of radio‑astronomy observations. However, to keep pace with the accelerating proliferation of wireless services and low‑Earth‑orbit satellites, the community will need more systematic, automated, and statistically robust monitoring frameworks, as well as stronger coordination between astronomers, spectrum regulators, and technology providers.