As a result of this choice, manufacturers can make relatively low-cost adapter boxes for existing TV sets, and broadcasters who charge for viewing can afford to give the boxes away. Picture quality and receiver cost are not the only differences between the European and North American terrestrial systems. In this modified amplitude modulation system, the lower sideband is virtually eliminated and only the upper sideband is transmitted, leaving the signal bandwidth at 6 MHz. That sideband is switched at high speed through eight phase and amplitude states. But the broadcast can be corrupted by interference or multipath reflections, which mix the direct broadcast signal with delayed replicas.
Unwanted reflections arrive in the wide gaps between the bits and are rejected.
But this move would make existing U.S. digital television equipment obsolete, on both the broadcast and receiving ends. Lagging behind the UK in the digital rollout is mainland Europe. Countries like the Netherlands are heavily cabled, and the Soviet Union's breakup has left Eastern countries strapped for cash. Sweden and Spain have now launched DVB terrestrial services, but consumer interest is less than in the UK as adapters are not free. A Babel of standards Outside Europe and the United States, there is a new Babel of different standards.