SAN MATEO, Calif. - The 8-VSB digital TV receivers specified by the U.S. Advanced Television Systems Committee (ATSC) must be refined to improve terrestrial DTV reception, particularly indoor reception, according to a recently completed study by the Communication Research Centre Canada (CRC).

The draft report of CRC (Ottawa) adds another layer of criticism to the U.S. industry standard already subject to divisive arguments over the need to add an alternative modulation scheme to ATSC's chosen U.S. digital TV standard, 8-vestigial sideband. Some broadcasters and industry observers have reportedly complained of the poor reception provided by today's terrestrial DTV signals in the United States.

Working in conjunction with Industry Canada Broadcast Planning and Policy Directorate and the Canadian Digital Television Inc., CRC carried out laboratory and field tests to evaluate the performance of 8-VSB receivers.

Half rate

Reliable indoor DTV reception was found at only about 50 percent of the 43 sites visited for the tests, which had used simple set-top antennas, according to the draft report. Indoor reception of DTV failed at 28 percent of the sites that used either a passive or active antenna due mainly to a combination of multipath and low field strength, the report said.

The report noted, however, that the 8-VSB receiver field tests found much better reception for sites using an outdoor 10 meter high antenna. In those circumstances, "DTV could not be received at only 4 of the 46 sites visited, mainly due to low field strength," the report said.

The ATSC put together a task force earlier this year to determine what adjustments if any should be made to the current 8-VSB modulation standard. The task force was to assess the 8-VSB modulation scheme chosen by ATSC, study current applications and requirements from broadcasters' perspectives, and develop a common methodology for field testing.

To date, the ATSC has closely guarded the results of its field tests, which were carried out last summer. Nor has the group released any progress report or details of the task force's work, due to a nondisclosure agreement signed by ATSC members.

CRC could not be reached for comment by press time.