GMRT faces signal interference from telecom operators

After over six years, the Pune-based Giant Metrewave Radio Telescope (GMRT) is finally free from interfering radio signals produced by cell phone towers owned by Reliance Jio Infocomm Limited (RJIL), located within 30-km vicinity of the international facility.

But, according to sources, the international scientific facility is now facing fresh trouble in the form of unwanted signal interference from cell phone towers owned and operated by other mobile phone operators. The latest errant operators are Bharti Airtel and Bharat Sanchar Nigam Limited (BSNL), which have mobile phone towers in the locality.

Located in Pune district’s Junnar taluka, the GMRT is a project by the Department of Atomic Energy (DAE) that is operated by National Centre for Radio Astrophysics (NCRA) of the Tata Institute of Fundamental Research (TIFR). This unique telescope, comprising 30 antennas fitted with sensitive signal receivers, operates in the 100-1500 Mega Hertz (MHz) frequency bandwidth.

Used to study the Universe and its evolution, the GMRT has led to a number of path-breaking discoveries. Operating since 2000 and known for its unique abilities to cover low radio bandwidth, GMRT is a much sought after telescope, with scientists from more than 30 countries benefiting from its usage.

The GMRT commands special protection from all kinds of radio interference generated from man-made sources such as local industries, high-voltage power lines and mobile phone towers in the vicinity, as well as other telecom services in the 100-1500 MHz range.

However, during the telescope’s regular operations, sometime in 2016, NCRA authorities noted radio signals in the 800-900 MHz range emerging from RJIL’s towers, significantly corrupting data quality. Several planned astronomical projects, which used this frequency range, had to be stalled due to fear of poor data quality, resulting in an overall threat to the telescope’s scientific potential. The Indian Express had first reported about these problems in August 2021.

Subsequently, NCRA authorities raised the issue both with RJIL and the Department of Telecommunication (DoT). The root cause was traced to be the DoT’s erroneous spectrum allocation to RJIL in 2016, wherein it allowed the telecom company to operate in the 800-900 Mhz range.

It took five years of repeated pleas and meetings between high-level stakeholder, from 2016 to 2021, for DoT to finally take corrective measures. In mid-2021, the Telecom Ministry issued orders allocating alternate bandwidth to RJIL outside the 800-900 MHz range, saving the GMRT from recording corrupt data.

After receiving DoT’s corrected spectrum allocation order, RJIL, in February 2022, started switching out of the earlier bandwidth. This task was completed swiftly and by mid-May, GMRT authorities confirmed zero interference from RJIL towers. During these months, operations of about 160 RJIL towers were shifted to the newly-allocated frequency.

“RJIL promptly complied with the DoT’s orders and cooperated with us in this matter. Our teams have verified all the incoming signals and have confirmed that there is no interference emanating from RJIL towers up to 30 km, the agreed upon protection zone around GMRT,” said a senior official of the GMRT facility.

However, earlier this year, the GMRT team discovered additional interference signals at around 900 MHz. These were traced to mobile phone towers in the GMRT protection zone, mostly from Bharti Airtel but also from BSNL-owned towers.

But this time, before any further scientific data loss, NCRA officials initiated talks with the two telecom companies, according to sources.

A senior NCRA official told The Indian Express that while Bharti Airtel extended cooperation initially, lately their reminder requests have fallen on deaf ears. Several towers of Bharti Airtel are still transmitting in the 900 MHz band, said a scientist.

Interestingly, there exists a Memorandum of Understanding (MoU) between the NCRA and Bharti Airtel since 2005, which underlines that Airtel’s operations should only be in the 1800 MHz band in the GMRT protection zone.

The GMRT official shared, “Recently, we even shared a copy of the MoU and reminded Bharti Airtel about the operational agreement in the region, but we are yet to get the full desired response from Airtel officials — only a few towers in the GMRT region have been switched to 1800 MHz. We now plan to escalate the issue with DoT’s Wireless and Planning Wing, and also within Airtel.”

An officer from Bharti Airtel (Maharashtra-Goa circle) said the telecom company has received an email in this regard on Wednesday. “About four months ago, we switched off five towers located within 2 km of GMRT. Thereafter, we had no communication with the GMRT team. On Wednesday, we received another email from GMRT about this matter, informing us about continuing signal interference. We need to check the matter and will deploy teams to do so.”

The officer said this was an ongoing process and Airtel will now take up dismantling of towers located at distances beyond 2 km.
Lower-level signals from BSNL towers have also been noted around GMRT in recent years. “But BSNL has been notified about this interference and they have agreed to cooperate,” said the NCRA official.

“BSNL has co-operated in the past every time we have approached them. We are expecting full cooperation from them in this matter too,” added the GMRT official. Indian Express