Zeroing on the criminal conspiracy relating to 2G scam among corporates, CBI is preparing a list of all ineligible telecom companies which had got the licences in 2008.

Besides, CBI is conducting a "microscopic examination" of a deal between Tata Group's real estate and infrastructure development arm Tata Realty and Infrastructure and Unitech whereby the latter had received a loan, which the agency claims, have been diverted, official sources said.

Corporate lobbyist Niira Radia is likely to be summoned again to the CBI in connection with the case for allegedly playing an important role in the deal, they said.

CBI has roped in the enforcement directorate officials to help it in locating the money trail and violations of Foreign Exchange Management Act (FEMA) and stake holding-patterns in some of the firms which acted as front for other telecom companies.

Sources said the CBI has decided to send Letters Rogatory (LRs) to two countries -- Cyprus and Norway -- to find out source of funding of telecom firms who were awarded spectrum.

A Letters Rogatory is a formal request issued by a competent court to a foreign court and processed by the ministry of external affairs on behalf of the investigative agencies to obtain information about individuals and entities.

"A list of ineligible firms is being drafted and its findings on criminal conspiracy/culpability will be finalised within two weeks' time," a CBI official said.

CBI, which is directed to file chargesheet by March 31 by Supreme Court, is likely to question DMK MP K Kanimozhi, who is the daughter of Tamil Nadu chief minister K Karunanidhi, in connection with the scam, they said.

Sources said CBI sleuths have found irregularities in funding Rs 214 crore to Kalaignar TV, a regional channel operational mainly in Tamil Nadu in which Karunanidhi family members allegedly have majority stakes, by DB Realty.

Earlier, the CBI had questioned R Krishna Kumar and Sanjay B Ugale, chairman and managing director, respectively, of Tata Realty and Infrastructure, Anil Sardana, former CEO of Tata Teleservices Ltd.

The CBI had also questioned Sanjay Chandra of Unitech on issues relating to offloading of majority stake to Norway based company Telenor after getting 2G spectrum license.

CBI is probing whether Tata Real Estate had paid Rs 1,600 crore to Unitech for a land deal at a time when the the real estate company was applying for 2G licence in 2007.

Comptroller and Auditor General (CAG) had in its report presumed losses to the tune of Rs 1.76 lakh crore in distributing spectrum to certain telecom firms due to certain procedural lapses.