Acting on secret information from amateur radio operators, officers from the Sagar police station raided these centres.

Praveen Kumar, SP (South 24 Parganas) said: “We raided and dismantled six radio stations. Four persons were arrested. These stations have been running for long.”

A huge number of music CDs, DVDs, microphones and six radio transmitters and high frequency antennae were seized from these offices. The operators — Anukul Shaw, Shanatan Jana, Srikanta Pramanik and Gaur Chandra Maity — were in their early twenties. Jana runs a radio repair shop in his neighbourhood.

A year ago, amateur HAM radio operators had warned the monitoring station at Gopalpur, in South 24 Parganas, about unauthorised radio stations.

The monitoring station is under the jurisdiction of the Department of Communications, Government of India. The monitoring station had filed a police complaint last year, but it had been difficult to locate the base stations then. This year, the police succeeded in tracking them down.

In general, the makeshift stations operate by procuring indigenous transmitters. “Transmitter circuits can be readily made at homes. The radio operators then procure these transmitters and the entire station could come up for an investment of Rs 5000 only. Then they are free to air music, organise request shows and make revenues from advertisements,” said an amateur radio operator. The operators make brisk business round the year airing local ads.

These operators operate in the medium wave in the range of frequencies 565 KiloHz to 1600 kiloHz used for broadcasting services like All India Radio.