NHK and the National Association of Commercial Broadcasters in Japan will start Monday to block attempts by viewers to illicitly duplicate digital television programs for commercial purposes.

The duplication control will be applied to digital TV programs aired by both terrestrial digital broadcasters and broadcasting satellites, according to NHK and the nation's biggest grouping of private TV broadcasters.

NHK and the member broadcasters of the association will mingle special antiduplication signals with conventional signals that make up the digital images and sounds of their programs, they said.

The special signals will make it impossible for people with digital TVs and special tuners for receiving digital signals to watch TV programs, unless they insert a B-CAS card into their digital TV sets.

B-CAS cards are distributed to owners of digital TV sets at the time of their purchase.

The mingling of antiduplication signals is designed to block illicit duplication of digital TV programs, which are of extremely high image and sound quality, for commercial piracy and dissemination purposes.

The broadcasters want to help the producers of digital TV content shield their intellectual property rights and copyrights from commercial pirates, they said.

But the new device and antiduplication signals are expected to inconvenience some innocent TV users.

Some 20,000 users have already made phone inquiries, with a quarter of them complaining that they have already lost their B-CAS cards.

Some said they cannot understand why TV broadcasters and manufacturers have installed such an antiduplication mechanism and are broadcasting antiduplication signals.

The antiduplication mechanism has already drawn criticism from some quarters of the home electronics appliance industry, which apparently fear the new mechanism may eat into sales.