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.

<<< Back to September 27 - Issue 184

October 4, 1999 - Issue 185 Final Edition

DTV - New Motorola Module Technology Aims to Make DTV Affordable (Oct. 4)
In August, Motorola reported its MCT2100 8-VSB demodulator was able to deal with the multipath ensembles found in the Sinclair indoor reception tests in Baltimore. If the performance promises prove out in the real world, this will solve one of problems slowing acceptance of DTV. Now, Motorola has taken aim at what many consider a large impediment to widespread adoption of DTV - the high cost of recievers and set-top boxes. Today Motorola introduced the MCT5100 M-DTV(tm) module. The MCT-5100 module is designed to convert digital TV signals to the existing standard definition format. It uses an analog IF input, demodulates it with an integrated MCT2100, then decodes the MPEG video and outputs it in various video formats, Dolby Digital(r) 5.1 audio data and a serial control port are available.

Bob Stokes, Motorola's Director of Operations, Digital Television Operations, said "Motorola's M-DTV module makes digital television available to consumers, providing higher-quality video and audio at competitive prices that they're willing to pay. There are more than 20 million analog TVs sold in the U.S. each year, and the M-DTV module will allow manufacturers to leverage their experience in analog TV, as well as offer a digital TV at an attractive price." The Motorola Press Release - New Motorola Module Technology Puts DTV on Standard Televisions said that because the processing and control of the DTV is handled in the module, manufacturers will be able to "integrate the module into existing analog TV chassis with minimum changes to the existing design."

FCC Report Says Benefits of Changing DTV Standard to COFDM Would Not Outweigh the Costs (Oct. 4)
The FCC Office of Engineering and Technology (OET) released a report on its independent assessment of COFDM and 8-VSB for DTV transmission. The results generally agreed with those of earlier studies. COFDM has advantages in mobile and single frequency network performance and 8-VSB had advantages in spectrum efficiency (data rate), carrier to noise performance and transmitter power requirements. A News Release (nret9904) on the Report stated: "The OET study concluded that both systems have certain advantages and disadvantages and are both capable of providing viable DTV service. OET further concluded that, based on discussions with consumer equipment manufacturers and recent announcements by semiconductor manufacturers Motorola and NxtWave, reasonable solutions to the multipath issue and indoor reception problems raised by Sinclair are being developed and should be available in the near future."

The FCC study "examined and estimated the difference in service availability between COFDM and 8-VSB operation in the top-10 markets." The new release said "These estimates appear to indicate that the relative advantages/disadvantages of either system with regard to overall coverage are generally small and vary by market." The study concluded that "the multipath reception problems identified by Sinclair are solvable with improved adaptive equalizer performance and that a well-designed 8-VSB receiver should be able to provide satisfactory reception at the Sinclair locations."

The study found that reception in multipath environments depends on the adaptive equalizer performance of the 8-VSB receiver and suggested a minimum equalizer range of 22 ms and suggested larger ranges may be beneficial. The study said that the poor performance of 8-VSB receivers in the Sinclair indoor reception tests may have been due to the receivers having an adaptive equalizer range of 10 ms or less. However, the study stated that the reception problems identified by Sinclair "are solvable with improved adaptive equalizer performance and that a well-designed 8-VSB receiver should be able to provide satisfactory reception at the Sinclair locations." In support of 8-VSB, the study said its advantage in "signal strength and immunity to interference from impulse noise are also important factors in successful indoor reception." The FCC also said consumer electronics manufacturers indicated that "improved receivers will be available this fall and that further improvements will be introduced next year."

The OET Report references an Oak Technology report containing measurement data and observations from five sites in Baltimore. Samples of both the COFDM and 8-VSB signals were captured. The OET Report includes amplitude and delay length for echos at four of the sites. Several manufacturers used this data or data they captured during the tests to simulate reception conditions. The OET Report said, "These manufacturers have stated that their existing or future equipment would perform satisfactorily under these conditions."

The OET Report includes a lengthy report on industry and press discussions about the Sinclair tests and the viability of 8-VSB. Most of the comments supported retaining the 8-VSB standard. There was agreement that 8-VSB receivers were available now with better performance than those used in the Sinclair tests and additional improvements were coming. A table in the Report compares service availability in urban and rural areas using COFDM and 8-VSB. For example, the study showed a 3.69 percent gain using COFDM in Dallas-Fort Worth (the best gain for COFDM) and 1.6 percent loss in service availability using COFDM in Philadelphia (the worst loss for COFDM). The comparison assumed 80 percent of the urban center population would have a COFDM signal above threshold and 50 percent would have multipath where COFDM would work and 8VSB would not. This gave COFDM an advantage in urban areas. The 8-VSB fringe advantage was calculated by assuming a 4 dB transmitter power advantage for 8-VSB that extends coverage beyond that provided by COFDM. In the extended area, it was assumed that 50 percent of the population could receive 8-VSB and not receive COFDM.

The complete OET report, FCC/OET 99-2, "DTV Report on COFDM and 8-VSB Performance" is available from the FCC Web Site as a text file or a Microsoft Word document.

SATELLITE - ATSC Approves New Technical Standard for Transmission of DTV Over Satellite (Oct. 4)
The Advanced Television Systems Committee (ATSC) has approved a new standard, which, as stated in its Purpose, "defines a standard for modulation and coding of data delivered over satellite for digital television (DTV) applications. The data can be a collection of program material including video, audio, data, multimedia or other material generated in a digital format. It includes digital multiplex bit streams constructed in accordance with ISO/IEC 13818-1 (MPEG-2 systems), but is not limited to these and makes provision for arbitrary types of data, as well." In a Press Release, ATSC said "The new standard was created to encourage the production of standardized satellite transmission and receiving equipment for use by digital television networks and DTV broadcast stations. Benefits of this standard are expected to include better DTV signal interoperability between networks and broadcast stations, and broad competition in the supply of professional DTV satellite transmission and receiving equipment."

The ATSC document closely follows existing standards developed by the Digital Video Broadcasting (DVB) Project of the European Broadcast Union (EBU) for satellite transmission. Relevant DVB documents include EN 300 421 (for QPSK) and prEN 301 210 (for QPSK, 8PSK and 16QAM). The tables included in the Annexes provide practical information for designing DTV satellite transmission systems. Annex B contains examples of possible uses of the system, showing the data rate capacity of the various modulation methods in various bandwidths with different coding schemes. For example, Table B.5 shows a 36 MHz satellite transponder is able to carry two 19.39 Mbps data streams using QPSK and 5/6 coding, three 19.39 Mbps data streams using 8PSK and 5/6 coding or four 19.39 Mbps data streams with 16QAM and 3/4 coding.

This standard A/80 is available on the ATSC Web site.

FCC Commences Rulemaking to Establish LPTV Class A "Primary" Service (Sept. 29)
The FCC has released a Notice of Proposed Rule Making (NPRM) regarding the Establishment of a Class A Television Service (MM Docket 99-292). While the NPRM is mostly concerned with the general amount of protection from interference and displacement to be granted Low Power TV stations that qualify for Class A status, it includes requests for comments on specific interference ratios and power levels for Class A TV station. Class A stations would have to be considered in interference studies for new or modified full service analog and digital stations under several of the proposals.

The FCC NPRM tracks a bill working its way through Congress that would mandate the establishment of a Class A LPTV service. It presents a wide range of options for protection of Class A stations. One proposal would use mileage separation to determine protection, while another would only protect the actual contour of the Class A station. The NPRM also asked in what situations, if any, should modifications to the DTV Table of Allotments be allowed to displace Class A stations.

Establishment of a Class A LPTV service will require expanding the station database used when performing OET-69 interference analysis. If the interference criterea adopted for Class A stations does not match that for full service DTV and analog stations, software based on OET-69 may have to be modified. Comments on this NPRM will be due 60 days after publication in the Federal Register,, with reply comments due 90 days after publication.

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DTV - News from CEMA DTV Summitt - DTV Sales Exceed 50K, Buyers Happy (Sept. 29)
The Consumer Electronics Manufacturers Assocation (CEMA) released data at the fifth DTV Summit showing digital television (DTV) sales to dealers exceeded 50,000 at the end of August. CEMA President Gary Shapario reported ""DTV is moving forward at a promising pace and we expect continued success in the third and fourth quarter." CEMA's Vice President of Market Research, Tood Thibodeaux, said preliminary results from CEMA's research on DTV showed consumer awareness of DTV increased from 60 to 85 percent since last March. Fifty-one percent of consumers surveyed expected their next TV purchase would be a digital set. If extrapolated to all TV purchasers, this would translate to 46 million households purchasing a DTV over the next eight years.

Picture resolution was the highest factor in DTV purchases - ranked at 95 percent. Thibodeaux explained, ""The questions consumers are asking retailers about DTV are positive - when will it be available? How will it work with current equipment? What are the differences between HDTV and SDTV? And retailers report that about 85 percent of consumers who see HDTV are impressed or very impressed with the technology." A survey of actual DTV owners found 95 percent of those surveyed would make the same purchase again.

For reports on other topics discussed at the DTV Summit, refer to the CEMA Press Release.

OTHER Items of Interest

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Last modified October 5, 1999 by Doug Lung dlung@transmitter.com
Copyright 1999 H. Douglas Lung