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KOLKATA: Suspicious signals in coded languages in an around Kolkata for the past few weeks have been intercepted by amateur radio ( Ham radio ) operators, prompting authorities to deploy round-the-clock monitoring of radio signals.

The first such incident came into light a few weeks ago just ahead of Diwali, after an amateur Ham radio operator picked up suspicious radio signals and unauthorised radio communication in coded languages from areas in Sodepur in North 24 Parganas district.

Since then, such signals were picked up from Chuchura in Hoogly district and Sealdah in Kolkata at a specific time in the night.

Areas where these signals were received are within 25-30 km radius of Kolkata.

Alarmed over the suspicious signals, the radio operators informed police officials, central agencies and the ministry of communication about this.

"For past few weeks especially after midnight we have been hearing such coded conversations. The whole thing is highly suspicious because whenever we tried to converse with them, there was no response. And when we asked them about their identity, there was total radio silence," said Ambarish Nag Biswas, secretary of Bengal Amateur Radio Club.

"Those who were communicating on the radio frequencies alluded to Pashto accent but we couldn't identify the language. I was first alerted by a fellow Ham radio club member who overheard such conversations," he told .

Pashto is a language widely spoken in Afghanistan.

Biswas said after the incident came into light, they had written to the Union Ministry of Communication and Information Technology, highlighting the strange signals and the suspicious mode of coded communications.

"We submitted details of our findings to International Wireless Monitoring station, police and central agencies. We were asked to continue monitoring and try to locate the source of the communications," he said.

The International Wireless Monitoring Station of Eastern region was pressed into service to track the signals.

When contacted, ADG (Telecommunication) of West Bengal Police, Debasish Roy said he is aware of the issue about suspicious signals in the coded language.

"We are aware of it and looking into the issue. We have sent the details to the Directorate of Coordination Police Wireless (DCPW) in New Delhi for necessary steps," he said.

DCPW is a wing under Union Ministry of Home Affairs.

A Kolkata-based senior official of International Wireless Monitoring Station said they have initiated a monitoring of the radio signals and the frequencies in which the conversation took place and will keep a tab on these for some time.

Intelligence Bureau officials here, however, didn't rule out terror outfits using such frequencies to communicate among themselves, as mobile networks can come under surveillance.

"It is not unnatural for extremists groups to communicate through these Ham radio frequencies as this mode is quite unconventional, unlike mobile networks or emails, which can come under surveillance. We will look into it," said a senior IB official, adding such kind of unverified communication in radio frequencies are often heard along the Indo-Bangla border.

In 2016, Ham Radio operators had picked up suspicious signals in coded Bengali and Urdu languages along the India-Bangladesh border in Basirhat and Sunderbans region.

Ham radio uses radio frequency spectrum to exchange messages with other radio operators. Each one of them are assigned a call sign for identity. The Ham or amateur radio operators are licensed to conduct such communications under specific radio frequencies by the Union Ministry of Communications and IT.