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Bad Spectrum Allocation Affecting Data Quality at Telescope, Scientists Say

Bad Spectrum Allocation Affecting Data Quality at Telescope, Scientists Say

Two of GMRT’s 30 dishes. Photo: GMRT website

  • The Giant Metre-wave Radio Telescope captures faint radio signals coming from distant parts of the universe.
  • It has rights to operate in a spectrum around 900 MHz for astronomical data, but the government allocated Reliance Jio frequencies in the 800-900 MHz band.
  • The result is signal interference that astronomers say is affecting use of the telescope and their work.

New Delhi: The Department of Telecommunications (DoT) has allocated airwaves in restricted frequency bands to Reliance Jio, which has deteriorated the quality of data available for scientific research produced by the Giant Metrewave Radio Telescope (GMRT) in Pune, according to Indian Express.

The GMRT is the world’s largest radio telescope operating in the metre-wavelength range of the radio spectrum, for astronomy research. Its 30 dishes capture very faint radio signals coming from distant reaches of the universe.

For example, in June 2021, scientists announced that they had measured the mass of atomic hydrogen present in the universe nine billion years ago using data collected by the GMRT.

Located about 80 km north of Pune, off the Pune-Nasik highway, the GMRT was built by the Tata Institute of Fundamental Research and operated by the institute and the National Centre for Radio Astrophysics (NCRA).

Celebrated astronomer Govind Swarup led the team that conceived of and designed the GMRT, and helped build it in the 1990s. Swarup passed away last year at the age of 90.

The GMRT can receive signals of frequencies in the range 100-1500 MHz. The telescope is actually an array – it consists of 30 steerable parabolic dishes, each 45 m wide, arranged in a giant ‘Y’ shape.

Scientists picked its location after an “extensive search in many parts of India”, according to the GMRT website, for a place free of electromagnetic signals that could interfere with the radio signals the GMRT is looking for.

Also read: S.C. Tapde: Of Antennae, Telescopes and an Engineer for All Seasons

The site selection criteria included a “geographical latitude sufficiently north of the geomagnetic equator in order to have a reasonably quiet ionosphere and yet be able to observe a good part of the southern sky as well”.

Scientists also optimised the number and configuration of dishes to meet astrophysics objectives that require sensitivity at “high angular resolution as well as ability to image radio emission from diffuse extended regions”.

But, according to scientists who spoke to Indian Express, these considerations have been undercut by the DoT’s negligence in allocating spectrum. The GMRT has a protected right to the 900 MHz band, but scientists alleged that the government allocated Reliance Jio Infocomm Limited (RJIL) 800-900 MHz frequencies.

One unnamed NCRA scientist told the newspaper that though RJIL had been operating in the region even earlier, the NCRA noticed “significant signal interference” only in 2016. The body then informed RJIL of the issue in 2017.

Strong signal interference generated by Reliance Jio’s operations, NCRA officials said, had permanently damaged large datasets. Scientists also said they had been forced to abandon some observations using the telescope.

The NCRA approached the DoT in 2018, asking it to allocate alternate spectrum beyond the 800-900 MHz range to Reliance. It also encouraged telecom companies at large to operate at frequencies around 1,800 MHz.

Some of the GMRT’s dishes. Photo: GMRT website

However, while the DoT had reportedly assured the scientists of a “positive solution” in 2018, it isn’t made a final decision yet – despite multiple follow ups.

“We urge DoT to intervene at the earliest and protect GMRT from suffering further data quality losses,” a scientist told Indian Express.

According to the US National Radio Astronomy Observatory (NRAO), radio signals of interest from outer space are typically millions or billions of times weaker than the signals that communication systems use.

“For example, a cellular telephone located on the Moon would produce a signal on Earth that radio astronomers consider quite strong,” according to the NRAO. “Because the cosmic radio sources are so weak, they are easily masked by human-made interference.”

Also read: Fewer Stars Are Being Born Today Than Before. A Pune Telescope Might Know Why.

Transmissions to and from cellular telephones and Wi-fi networks, among other systems, use radio signals. And, the NRAO says, the “inadequately engineered transmitters” that send these signals endanger ground-based radio astronomy.

On the flip side, good engineering can prevent or minimise interference:

“Spillover from overly-broad transmitters and other unintended signals do nothing to improve the performance of a communication system. Technology readily available to radio engineers can eliminate or drastically reduce these unwanted signals that threaten radio astronomy. It is especially important that such interference-reducing technology be included in orbiting satellites.”

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