Radio frequency interference is emerging as a threat to astronomy. Examine the challenge and India's technological responses.

Radio frequency interference (RFI) is unwanted man-made radio noise. It now drowns out the faint cosmic signals that astronomers try to detect. Detecting the 21-cm hydrogen signal has been called "like hearing a whisper in a stadium full of noise" [2]. The problem is scientific, technological and regulatory, and India is responding on all three fronts.

The challenge

• Many sources: FM stations, WiFi, mobile towers, radar and satellites all emit RFI [3].
• Band overlap: early-universe hydrogen studies use low frequencies near 100 MHz, which is where FM broadcasting sits [3]. On Earth, FM transmissions overwhelm these observations [2].
• Space is no escape: RRI's STARFIRE model shows that RFI from Earth reaches LEO, MEO and GEO (400–36,000 km) [3]. The ionosphere also distorts signals seen from the ground [2].
• Growing demand for spectrum: NFAP-2025 allocates 8.3 kHz–3000 GHz and adds the 6425–7125 MHz band for 5G/6G [4]. As telecom use grows, less of the radio sky stays quiet.
• Cost of cleaning the data: the CHIME team needed new techniques to remove noise from human technology, then spent over a year testing its hydrogen detection [1].

India's technological responses

• Measure: RRI's STARFIRE algorithm (Simulation of TerrestriAl Radio Frequency Interference in oRbits around Earth) uses FM-transmitter data from six countries. It found that lower orbits pick up signals from fewer transmitters, which guides the early phase of PRATUSH [3].
• Escape: PRATUSH, RRI's planned space payload to detect the early-universe 21-cm hydrogen signal, will orbit on the Moon's far side. This is "the most radio-quiet place in the inner Solar System" [2].
• Miniaturise: a Raspberry Pi-based single-board computer coordinates PRATUSH's antenna, receiver and FPGA chip within tight size, weight and power limits [2].
• Filter: RRI scientists are part of CHIME, whose new analysis techniques separated the hydrogen signal from man-made and instrument noise [1].
• Collaborate: India approved ₹1,250 crore for the Square Kilometre Array (SKA), a global radio telescope project [5]. It is a founding member of the SKA Observatory and led the design of its Telescope Manager system [6].

Earth noise → Measure (STARFIRE) → Filter (CHIME) → Escape (PRATUSH, lunar far side)

Fig: India's three-step answer to RFI

In short, RFI is growing as fast as the spectrum economy that creates it. India's answer has been to measure it, filter it out and move beyond it. NFAP revisions already involve academic stakeholders [4]. Next, the Department of Telecommunications should use STARFIRE-type data from DST and RRI to protect key astronomy bands and radio-quiet zones. That would let India's digital growth and its astronomy ambitions go forward together.