KOLKATA: Suspicious signals in coded Bengali and Urdu languages along the India-Bangladesh border in past few months have raised suspicion over extremists using this unconventional mode of communication, prompting authorities to deploy Ham radio operators on round-the-clock duty.The incident first came into light in June after amateur Ham radio operators picked suspicious radio signals and unauthorised radio communications in coded Bengali and Urdu in Basirhat and Sunderbans region.Alarmed over the incident, the operators informed the Centre following which they were called to an international monitoring centre (Radio) and asked to track the signals.A team of 23 Ham radio operators are now on round-the- clock duty trying to track the exact location of radio signals."The incident is highly suspicious and threat to security. Because whenever we tried to converse with them, they have stopped talking. Again after certain point of time they start their communication in coded Bengali and Urdu language," said Ambarish Nag Biswas , secretary of Bengal Amateur Radio Club."Those who were communicating on the radio frequencies had a distinct Bangladeshi accent. I alerted my radio club members and they too received such conversations. This kind of communication started in June and was going on till Durga Puja," he told PTI.Biswas said after the incident came into fore they had written to the Union Ministry of Communication and Information Technology, highlighting the strange signals and the suspicious mode of coded communication."After the letter was sent to the Union ministry, we were called for a meeting by the officials of the international monitoring station in Kolkata, where other senior officials were also present. We submitted details of our findings. We were asked to continue monitoring and try to locate the source of the communication," he said.After days of toil, Biswas and his team found out the location of the radio communications to be Basirhat area in North 24 Parganas and Sunderbans in South 24 Parganas."Such communications take place at night and the source is the bordering Indo-Bangla areas," he said.The Ham or amateur radio operators are under the Union Ministry of Communications and are licenced card holders to conduct such communication under specific radio frequencies.When asked how he found the communications suspicious, Biswas said during 2002-03 too he had overhead such communication and later on police after tracking the signals had arrested six extremists from Gangasagar in South 24 Parganas."At that point of time too I had overheard such suspicious conversation in coded language. I had approached the then Chief Minister Buddhadeb Bhattacharya, who instructed police officials to get in touch with me. After tracking those signals, police arrested six extremists from Gangasagar," he said.State IB officials, however, didn't rule out terror outfits using such frequencies to communicate among themselves, as mobile networks can come under surveillance."The border of India-Bangladesh near West Bengal is porous. Smugglers and extremists try to exploit it fully. 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," a senior IB official said.