Welcome to RF Current, a weekly electronic newsletter focusing on Broadcast technical and F.C.C. related issues. This newsletter is part of The RF Page @ www.transmitter.com, a web site devoted to TV Broadcast RF engineering. For more information see the What is... guide to the R.F. Page site.

Issues are dated each Monday, although recently I've needed an extra day or two to complete each issue. Articles may be posted earlier if time permits or if there is a major, breaking story.

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March 20, 2000 - Issue 206 Final Edition

DTV - ATSC Responds to Brazil SET/ABERT DTV Test Report (Mar. 20)
The ATSC responded to the SET/ABERT DTV tests in Brazil with a paper showing the test results actually demonstrated the ATSC 8-VSB DTV modulation system outperformed the DVB-T 2K COFDM modulation method. It discounted tests results for the 8K COFDM and ISDB modulation methods because they were tested at only some of the locations where the 8-VSB and 2K COFDM systems were tested. In several areas, ATSC's response to the Brazilian tests matched the response to the Australian DTV tests, where COFDM was selected. In both cases, the tests showed the ATSC 8-VSB system had an advantage over COFDM in threshold performance. With regards to the SET/ABERT testing, the ATSC response said "With respect to field tests, extensive, statistically reliable data was only collected for two systems: the ATSC/VSB system and the DVB 2k system. In both these field and laboratory comparisons, we believe that the data convincingly shows that VSB outperformed the DVB 2k system."

Regarding the COFDM 8K and ISDB testing, ATSC said, "Unfortunately, the limited number of sites at which these two systems were tested, and the manner in which the sites were selected, mean that the data is insufficient to justify the conclusions reached about these systems. We are concerned that conducting tests of these two additional systems at only a few selected sites that were difficult for VSB, while automatically assuming that these systems would function properly at other sites, does not yield an accurate or reliable basis for comparison to other systems. Second, the wide variation in results for the same site at different times makes clear that such sweeping assumptions are not valid. In sum, a reliable comparison of the overall performance of the various systems cannot be achieved using the field test data collected, which for ISDB and DVB 8k came from only a few selected sites."

ATSC noted that for the SET/ABERT testing, the area of concern had a radius of about 30 km, while in the U.S. coverage over a radius of 85 km is often necessary to duplicate analog coverage. "Even so, for the power levels used in the São Paulo field tests, the approximate 5 dB raw coverage advantage of VSB over all of the COFDM systems was evident in VSB's superior performance as compared to the DVB 2k system, even at these relatively short distances." ATSC also pointed out that "interference limited" channel planning is key and that "This means that while performance in the presence of multipath impairments will continue to be important, it should no longer be the primary driver of ANATEL s transmission system selection. Again, the channel assignment process must become an integral part of the system selection process." In addition, ATSC said "although São Paulo is certainly an important area to consider, ANATEL should carefully consider the extent to which conclusions reached for São Paulo can be extrapolated to other regions of Brazil. The significant raw coverage advantage of VSB may well be crucial in other areas of Brazil."

The ATSC response pointed out an interesting aspect of the reception conditions at the "six critical sites". ATSC noted that "the distinguishing attribute at difficult sites usually was not strength of ghosts, but length of ghosts. In the majority of sites where both DVB 2k and VSB failed, systems with longer ghost capability worked much better. This is an important finding, because it suggests that improvements now being incorporated in VSB receiver designs can be expected to address these shortcomings and improve the performance of VSB at the identified test sites. By contrast, improvements in the performance of the COFDM systems will continue to be constrained by the hard choices that must be made between the length of ghosts that can be handled and the delivered data rate."

The ATSC also pointed to third and fourth generation VSB receivers that were not mentioned in the SET/ABERT report that promise to do better in the locations where the problem was long ghosts rather than strong ghosts. The third generation design is available now and ATSC said the fourth generation design should be available in mid-April. The third generation design was tested by SET/ABERT, but the results were not reported.

Please refer to the ATSC Comments on the SET/ABERT Report. It contains a table that shows how DVB 2k, DVB 8k ISDB and ATSC methods compared in the laboratory tests. ATSC was the winner in 14 of the 19 tests. The ATSC comments and associated data linked to on the Comments page are Adobe PDF files.

FCC Begins Inquiry Regarding Software Defined Radio (Mar. 17)
The FCC approved a Notice of Inquiry (NOI) asking for public comment on software defined radio (SDR) equipment. Software defined radios can be reprogrammed to transmit and receive over a wide range of frequencies using virtually any transmission format. One device could be reprogrammed to work with cellular services, PCS and other wireless services worldwide. The FCC believes this flexibility could "promote more efficient use of the spectru, expand access to broadband communications for all persons and increase competition among telecommunications service providers."

The flexibility of SDR also impacts a number of the FCC's functions, including spectrum allocation, spectrum assignment and equipment approval. As a result, the FCC NOI solicits information "about the state of SDR technology, interoperability issues, spectrum efficiency issues, equipment authorization processes, and other issues to assist the Commission in deciding whether to propose rule changes as a result of the developing SDR technology." Some of the specific issues raised in the NOI include how SDR might improve interoperability among communications systems, whether SBR would allow wireless operators to change to a more efficient transmission system with requiring replacement of base station transmitters or field units, whether SDR equipment could be designed to monitor the spectrum and chose open channels for transmission, and what the implications are for the current spectrum allocation model. With regards to regulations, the FCC invited comment on whether FCC approval should be required for the radio hardware, the software or a combination of the two and whether an authentication could be designed using special codes in the software.

The FCC Technological Advisory Council is also reviewing SDR technology. However, the FCC said the NOI was important "to obtain input on the subject from all interested parties to ensure that all viewpoints are represented." A more complete summary is available in the FCC News Release FCC Begins Inquiry Regarding Software Defined Radio (nret0004). Also see the complete text of Notice of Inquiry released March 21.

SCIENCE - Study Finds Evidence of Association Between EMFs and Exposed Worker Suicide (Mar. 15)
A study conducted at the University of North Carolina, Chapel Hill found what appears to be a distinct association wbetween exposure to low frequency electromagnetic fields (EMFs) and suicide among electric utility workers. The study indicated electricians working for five U.S. power companies faced twice the expected risk of suicide, linemen faced one and one-half times the expected risk and power plant operators had a risk slightly lower than that expected. Younger workers appeared to be a greater risk and high, more recent exposures seemed to boots the chances of worker suicide. The study began with a group of 138,905 male U.S. electric utility workers.

One of the study's authors, doctoral student Edwin van Wijngaarden, explained, "We believe this work is important because suicide is the eighth leading cause of death in the United States, and many people in this country are exposed to electromagnetic fields," van Wijngaarden said. "While these findings definitely do not prove EMFs cause suicide, they do indicate more research needs to be done on the effects of exposure on depression and suicide." van Wijngaarden said the reason why low frequency electromagnetic fields might contribute to suicide among chronically exposed workers is not known.

A report on the study appears in the April issue of Occupational and Environmental Medicine. Additional information is also available in the UNC News Release Largest study finds evidence of association between EMFs and exposed worker suicide.

OTHER Items of Interest

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