RF CURRENT

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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May 8, 2000 - Issue 213 Final Edition

DTV - ATSC Comments on Brazil Report Critical of ATSC 8-VSB Modulation (May 5)
Robert Graves, Chairman of the Advanced Television Systems Committee (ATSC) released comments critical of some parts of the 3rd Partial Report on DTV tests in Brazil from the SET/ABERT DTV Committee. In the cover letter to the detailed comments, Graves said ATSC believed the information "further substantiates our earlier comments..."

The comments were summarized:
  1. "The ATSC/VSB system certainly merits further consideration for Brazil's digital TV standard.
  2. "The ATSC/VSB system outperformed the DVB 2k system in the only statistically reliable portions of the SET/ABERT field test program.
  3. "The ATSC/VSB system outperformed ALL other systems in the laboratory tests - especially in the critical parameters that enable channel assignments for the new DTV service.
  4. "Recent and forthcoming advancements in VSB receivers will provide significant further improvements in the ability of the ATSC/VSB system to handle severe ghosting situations, such as those found in São Paulo.
  5. "The limited test data accumulated for the ISDB system and the DVB 8k system is still not sufficient to provide a basis for selecting either of them over competing systems. Complete and simultaneous testing of all systems is essential for obtaining the full information necessary to make the important decision about a digital television standard for Brazil.
  6. "The selection of a DTV transmission system must include assessments of DTV channel planning feasibility as an integral part of the decision process.
  7. "Interference-limitedl. channel planning is key, especially for the important area of São Paulo, and we believe this will be best achieved using the ATSC/VSB system.
  8. "Delivered data rate is crucial for HDTV and other video and data applications, and should not be sacrificed lightly or unnecessarily.
  9. "Significant economic factors should not be ignored in selecting a DTV system for Brazil. For example, we continue to believe that both professional and consumer DTV equipment, especially consumer HDTV equipment, will be more readily available from more suppliers at lower prices if Brazil adopts the ATSC DTV Standard for its digital television services."

The detailed comments listed the flaws in data collection and analysis in the 3rd Partial Test Report:
  1. "Many measured quantities and data points were not reported. (For example, margin measurements are not reported when impulse errors were frequent).
  2. "Unlike the earlier report, other data that serves to confirm measurements or to help evaluate results was not reported (received power and attenuator settings). These quantities should be recorded in order to verify the field strength, which is a strong determinant of reception success.
  3. "Often an improper assumption was made that only positive results were meaningful. This means that passes from previous tests were counted, as well as current passes. There was no consideration of the possibility of new failures at the previously tested and passed sites that were not retested. This is improper, as the data has clearly shown that variation of conditions at a given site can be quite large."

The detailed comments listed six areas of concern with the Brazil field tests:
  1. "For the only set of field measurements that were statistically reliable, and where the systems being compared offered a nearly equivalent payload data rate and capability of handling ghosts of roughly equivalent length, the ATSC system proved superior to the DVB system.
  2. "The limited field data for the DVB 8k and ISDB systems, and the inconsistent and inappropriate ways in which it was selectively combined with a handpicked subset of the original data, do not justify the broad conclusions implied by the unsupported graphic representations in the SET/ABERT 3rd Partial Report.
  3. "The antenna used for the SET/ABERT field tests was of specific benefit to the COFDM systems due to its low gain and very broad acceptance angle. A more conventional consumer antenna has much better gain and a narrower reception angle, and its use would have improved the reception performance of the ATSC/VSB system.
  4. "Additional data obtained for the DVB 8k and ISDB systems suggests that further improvement may well be obtained in ATSC/VSB receivers that embody longer equalizers, which are rapidly being introduced. Indoor tests were very subjective and do not appear to provide any reliable basis for drawing general conclusions about the performance of the various systems.
  5. "The gap filler test showed that the ATSC/VSB system can be used in this manner very successfully. The substantial improvement in reception at 'difficult' sites demonstrates the viability of using low power gap fillers with the ATSC system to achieve nearly universal coverage."

The ATSC comments repeated the need to assess the "ability of each system to provide an adequate number of DTV channel assignments...", noting, "Concern about one or two sites where reception may be problematic will quickly lose significance if existing broadcasters are unable to be assigned a channel with which to compete in the digital millennium."

The ATSC letter stated, "we strongly urge ANATEL to undertake a new series of statistically significant tests wherein data is taken at each site on each DTV system at the same time. We are preparing a list of suggestions for such testing, and we encourage you to obtain input from the other system proponents as well. In this manner, ANATEL will be able to ensure that its decisions are based on the most complete, relevant and accurate information."

The ATSC SET-ABERT Report web page includes the cover letter and links to the detailed comments on both lab and field tests. For information on the Brazil tests, visit the SET Home page, where you will find the Final Report on Digital Television Systems Brazilian Tests as an Adobe PDF file (testing.pdf) or a zipped file (testing.zip) for downloading. The SET Presentation at NAB 2000 is also available as a Powerpoint presentation (set.pps). It is also available in compressed format for downloading - set.zip.

FCC Experimental Actions for February 2000 (May 4)
The FCC Office of Engineering and Technology has released its list of experimental licenses issued from 2/1/00 to 3/1/00. Two of the actions look particularly interesting for TV broadcasters. The FCC granted Rockwell Collins license WB2XHU to operate in spectrum from 180-210 MHz (U.S. TV channels 8 thru 12), 476-608 MHz (TV channels 15-36) and 614-788 MHz (TV channels 38-66) "for the test, development and demonstration of a military radio communications system." Mobile operation was authorized at Fort Gordon and Fort Benning in Georgia; Fort Monmouth in New Jersey; Richardson, Texas and Cedar Rapids, Iowa.

Lockheed Martin received license WB2XFW to operate on 512-608 MHz (TV channels 21-36), 614-650 MHz (TV channels 38-43) and 650-806 MHz (TV channels 44-69) "for training and evaluation of telemetry equipment under Army contract." Operation is limited to portable and mobile operation within a one mile radius of 12506 Lake Underhill Road Facility in Orlando, FL.

Two companies received authorizations for antenna testing. Andrew Corporation was granted a license to operate in the 150 - 58,000 MHz range for development and testing of antennas at an outdoor test range in Orland Park, IL. Ball Aerospace and Technologies Corporation was authorized to use 800-960 MHz and 1850-2200 MHz for antenna pattern testing.

James E. Carlson received license WB2XGW to operate on 902-928, 2400-2483.5 and 5725-5875 MHz for testing spread sprectrum equipment for Internet connection in Humbolt and Mendicino Counties, California. Broadcast Microwave Services was granted permission to operate on portions of the 2 GHz, 2.5 GHz., 6 GHz, 7 GHz, 10-13 GHz, 18 GHz, 21 GHz and 40 GHz bands to demonstrate and test microwave equipment.

Information on these and other experimental license grants may be found in the FCC Public Notice - Experimental Actions - Report No. 323.

TECHNOLOGY - Plots Demonstrate Dramatic Improvement in GPS Accuracy (May 2)
On May 2, 2000 at approximately 0405 UTC selective availability was switched off on all GPS satellites. Selective availability (SA) was an error introduced in the GPS signal. The Interagency GPS Executive Board (IGEB) plotted the ellipsoidal height scatter of 24 hours of data (from 0000 to 2359 UTC) taken on May 2, 2000. IGEB has posted plots showing the dramatic improvement in accuracy in the first moments after the SA was switched off.

These diagrams are available at www.igeb.gov/sa/diagram.shtml. A useful source for detailed technical information is the Global Positioning System Overview by Peter H. Dana, The Geographer's Craft Project, Department of Geography, The University of Texas at Austin.

OTHER Items of Interest

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