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 December 13 - Issue 194
January 3, 2000 - Issue 195 Millennium(-1) Edition
- DTV - Motorola Field Test Results of New 8-VSB Chip Inconclusive (Jan. 3)
- Motorola has posted the preliminary results of tests of a prototype receiver using its new MCT2100 8VSB demodulator. The tests were conducted in Philadelphia PA, San Francisco CA and Washington D.C. RF Current attempted to quantify the results described in the reports posted on the Motorola web site. Because the data was incomplete and inconsistent, this was not easy. However, close study of the results showed that even with this advanced demodulator chip, reception is not guaranteed. In some cases, the problem appeared to be associated with individual channels. It appears effective radiated power does make a difference. In other cases, it was possible to easily receive some stations with inexpensive set-top antennas. The results currently posted on the Motorola web site are unlikely to satisfy either proponents or supporters of the ATSC 8VSB standard.
Motorola tested reception with a series of antennas, including a Radio Shack 2-bay bowtie and reflector, a Lexon set-top antenna with rabbit ears and a loop UHF antenna, a Bodar antenna (little detail on this one) and a yagi mounted on a mast that could be extended to 30 feet. Motorola considered digital reception unreliable if more than 2.5 uncorrectable MPEG-2 packets per second were received in a 20 second period. Because the preliminary test results do not specifically state whether reception was possible or not with each antenna, for this analysis I considered reception on any of these antennas a success. In some cases, the report indicates reception was possible, but also notes there were limitations. In these cases, if the Motorola report implied reception was usually reliable, I considered it a success. When a station or channel wasn't mentioned, I assumed no reception. At some of the locations tested, no stations were received. When no stations were received at a location, I dropped that location from this summary. Since the Motorola study did not compare reception with NTSC signals on a consistent basis, it is possible these sites were blocked from all signals and incorporating them into the summary would skew the results. To get a better understanding of the results, please take the time to download the test summaries from the Motorola web site.
The Philadelphia Pennsylvania tests looked at four stations: KYW (CBS) with 750 kW ERP on channel 26, WPVI (ABC) with 500 kW ERP on channel 64, WCAU (NBC) with 100 kW ERP on channel 67 and WTXF (Fox) with an unspecified ERP on channel 42. The WTXF CP shows an authorized ERP of 305 kW. The FCC engineering database did not provide antenna data for any of these stations. Tests were conducted at twelve sites. At one of the sites, no DTV statiosn were received. At the other eleven sites, all four stations were seen at one, three stations were receivable at two of the sites, two of the stations at seven of the sites and one at all eleven sites. In this market, KYW was clearly the leader - receivable in all eleven sites. WPVI was received reliably at seven sites. WCAU could be reliably received at only one of the sites. WTXF was somewhat better, being received at three of the sites. These results are not encouraging. Even if the two stations that performed the worst are dropped, the remaining two were receivable at only 64 percent of the sites where any station could be received. This drops to less than 60 percent if all the test sites are consider. The test report conclused:
"The field test data clearly reveals that multipath in the real world is much more complicated than
what we are able to generate in the lab with a 6-ray dynamic ghost simulator. The field tests also
revealed that the spectrum analyzer display is not always a good indication of the severity of a
multipath channel. We often observed channels which had a "reasonable" looking spectrum and
yet were unreceivable, while others had deep notches at particular frequencies and were
received without difficulty."
"It was revealing, though unfortunate, to find that in many sites (or antenna positions at a site), the
limiting factor preventing reception was multipath, not received signal power."
The Washington DC tests used WETA (PBS) channel 27, WUSA (CBS) channel 34, WTTG (Fox) channel 36, WJLA (ABC) channel 39 and WRC (NBC) channel 48. Effective radiated powers (ERP) were not specified, although WETA was listed as "very low power". The FCC database shows the ERP for the stations as: WETA - 75kW, WUSA - 646 kW, WTTG - 1,000 kW, WJLA - 646 kW and WRC - 813 kW. The Motorola report mentioned considerable problems with interference from the aural carrier from the WETA NTSC transmitter on channel 26. Ten locations were studied and reception of at least one station was possible at nine of the locations. Of these nine locations, all five stations were receivable at two of them, at least four of the stations at three of them, at least three of the stations at seven of them and at least two of the stations at eight of them. These results are better than those in Philadelphia. Over half of the stations could be received at 78 percent of the locations were any reception was possible. However, all of the stations were receivable at only 22 percent of the lcoations with any DTV reception. Only WTTG was receivable at nine of the locations. WUSA was next, at eight locations, followed by WJLA at five, WRC at four and WETA at three.
The San Francisco tests are interesting in that all of the stations tests are transmitting from the same site, all using an antenna manufactured by Dielectric. Motorola checked reception at 15 sites. At one obstructed site, it was not possible to receive any signals. At another, a bad cable prevented reception. At the remaining 13 sites, KRON (NBC) on channel 57 with 1,000 kW ERP was received. KBHK (UPN) on channel 45 with 206 kW was received at 11 sites. Motorola indicated that at some sites, KGO (ABC - channel 24, 561 kW), KPIX (CBS - channel 29, 1,000 kW) and KTVU (Fox - channel 56, licensed ERP of 501 kW) were received with "some [or few] segment errors". If these the "error" sites are considered as having successful reception, KTVU was received at 12 sites and KGO and KPIX at 11 sites. If the "error" sites are removed, KGO was received at 7 sites, KPIX at 6 and KTVU at 8. Overall, if "error" reception is not included, all stations were received at 3 of 13 sites, four stations or more at 5 sites and 3 stations or more at 11 sites. At least two signals were available at the 13 sites. IF the stations with some errors are included, reception of all 5 stations was possible at 8 of 13 sites, at least 4 stations at 11 of the 13 sites, and at least 3 stations at all 13 sites.
What do these results mean? Motorola did not pick easy sites for the tests, so some reception failure is expected. What is surprising the the difference in reception among stations, particularly with the D.C. and Philadelphia tests. Even though stations had very similiar facilities in San Francisco, variations between stations were obvious. In San Francisco, KBHK at 206 kW ERP outperformed all stations except for KRON in error free reception, inspite of being the station with the lowest ERP. More study will be necessary to determine if the differing reception is due to the transmission system or basic limitations in the 8VSB modulation method. In Philadelphia, the modulation wasn't the only issue. Motorola found some stations were simply too weak for reception.
This article attempted to derive quantitative data from Motorola's essentially narrative field reports. As pointed out earlier, the lack of data in the preliminary Motorola reports made it necessary to make some assumptions as to whether reception was possible for specific stations at specific sites. If these assumptions are wrong, the data will change. Please refer to the reports Motorola has posted on its web site to draw your own conclusions.
Links to the reports (in Adobe Acrobat format) and photos are
available on the Motorola Summary of Test Results on the MCT2100 ATSC 8-VSB Demodulator page. In the reports, Motorola does not draw any conclusions on the suitability of 8VSB for terrestrial digital broadcasting. While Motorola has devoted substantial resources into improving 8VSB reception, it is also developing chips for the DVB-T COFDM standard. In December, Motorola also updated information on its MC92308 DVB-T 2K Mode Demodulator and its MC92314 DVB-T 8K and 2K Mode Demodulator. Both chips will work in either a 6, 7 or 8 MHz channel. Therefore, it appears Motorola would have no reason to favor either 8VSB (ATSC) or DVB-T (COFDM) systems in its tests or reports.
- FCC - David J. Farber Named Chief Technologist (Jan. 3)
- William Kennard, chairman of the FCC, welcomed David J. Farber as the new Chief Technologist for the Federal Communications Commission. "The FCC, and, indeed, the entire country, are very fortunate to have the services of such a distinguished, world-class technology expert as Dave Farber at this time, as the FCC continues to tackle the complicated and increasingly technical issues involved in ensuring universal broadband access," noted Kennard. Farber is currently the Alfred Fitler Moore Professor of Telecommunications Systems at the University of Pensylvania. He is also Director of both the Center for Communications & Information Science & Policy and the Laboratory for Distributed Systems. Farber is a Fellow of the IEEE and holder of the 1995 SIGCOMM Award for lifelong contributions to the field.
Reaction from the computing and engineering community to Farber's appointment has been extremely positive. Farber is active in the technical community. His Interesting People mailing list, started twelve years ago, is relied apon by professors, hournalists and people working with information technology as a source of news and commentary. The best description of David Farber is in the Spring 1999 Penn Triangle article - Who is David Farber? by David Rosensweig. Slashdot, "News for Nerds, Stuff that Matters", ran a article Dave Farber Named FCC Chief Technologist that drew 31 comments from readers, most were positive Farber, some were negative on the FCC.
- SCIENCE - USGS Warns Geomagnetic Storms May Kick off the New Millennium (Dec. 28)
- The U.S. Geological Survey issued a News Release, Geomagnetic Storms May Kick off the New Millennium, that received attention as yet another threat in the new millenium. The News Release focused on the eleven year sunspot cycle, noting that the last great magnetic storm on March 13, 1989 at 3 a.m. EST, eleven years ago. USGS said that storm caused the collapse of the Hydro-Quebec power system in Canada. The collapse left about 6 million people without power. The sentence that appeared to interest most news editors was "The next peak in sunspot activity is expected to occur in early 2000 - perhaps just in time for the arrival of the New Year."
USGS continuously monitors the Earth's magnetic field through a network of 13 magnetic observatories. The information is usually available on the USGS web page at geomag.usgs.gov, however, when it was checked on January 9, 2000 it had been hacked and no information was available.
- FCC Satellite Applications (Dec. 23)
- The FCC released Report No. SAT-00030 - Satellite Policy Branch Information. PanAmSat filed an application to launch and operate PAS-24, to replace its PAS-6 satellite at 68.5 degrees East Longitude (EL). PAS-24 will have 24 36-MHz Ku-band transponders and 24 C-band transponders, with bandwidths of 54 MHz and 27 MHz. PanAmSat also filed an application to launch and operate a hybrid C/Ku-band Galaxy V-R at 125 degrees West Longitude (WL). The C-band capacity would serve as a replacement for C-band Galaxy V. PanAmSat asks the Commission waive its rules to permit it to include Ku-band capacity on this satellite with initiated a new processing run. PanAmSat requested authority to launch and operate hybrid C/Ku-band Galaxy IX-R to replace Galaxy IX at 127 degrees WL. As with, Galaxy V-R, PanAmSat requested a waiver to allow it to include Ku-band capacity on this satellite PanAmSat also asked for permission to launch and operate another replacement satellite, Galaxy I(H) to replace Galaxy I-R at 133 degrees WL. A waiver to allow Ku-band capacity was requested.
Loral Space and Communications LTD filed an application for modification of the milestone dates for its Telstar 8 satellite to April 30, 2002 for completion of construction and July 30, 2002 for launch. Loral Orion filed an application to modify its Orion F7 Ka-band satellite authorization at 89 degrees WL to allow it implement the Orion F7 authorization through the addition of a Ka-band payload to the Telstar 8 satellite. Loral filed another application to operate Telstar 8 at 89 degrees WL instead of 77 degrees WL and to redefine the coverage area to provide service throughout North and South America using separate switchable beams. Loral Orion Services requested that its Telstar 12 (formerly Orion 2) authorization be reassigned from 12 degress WL to 15 degrees WL, as necessitated by its coordination agreement with Eutelsat. Eutelsat has a satellite operating at 12.5 degrees WL.
- FCC Amends Table of Frequency Allocations (Dec. 20)
- The FCC, in a Memorandum Opinion and Order - Amendment of Part 2 of the Commission's Rules to Make Non-Substantive Revisions to the Table of Frequency Allocations (DA 99-2743) released today, amended the Table of Frequency Allocations (Table) found in Section 2.106 of the FCC Rules. The changes to the table do not change the allocations established by other FCC actions. They do, however, update the International Table in the regulations to reflect allocations found in the 1998 ITU Radio Regulations. Also, expired footnotes in the Table are removed, the special-use frequencies column of the Table is deleted and various typographical errors and omissions are corrected. The FCC Order said that, as a result of these actions, it will be able to place the Table on the FCC Web site and update the on-line Table soon after any amendents to the Table are released. The Order emphasized, "This ministerial action does not make any substantive change to any licensee's legal rights and responsibilities."
Some of the changes involve merging the Federal and Non-Federal Government Tables for frequencies bands that have exactly the same allocations and footnotes. The new Table adds allocations for the Medical Implant Communications Service (402-405 MHz), Dedicated Short Range Communications in the Intelligent Transportation System radio service (5850-5925 MHz), and the realigned allocations in the 36 GHz to 51.4 GHz band. The FCC also subdivided the upper edge of the UHF TV band, from channels 52 to 69, into two segments - 614 to 698 MHz and 698 to 746 MHz. A note explaining that the FCC is required to reallocate and auction the 698 to 746 MHz band by September 20, 2002. The Order stated that because their are petitions for reconsideration regarding the FCC's proposals for the 1990-2110 MHz and 2165-2200 MHz bands, the FCC made "only non-substantive revisions to the 1990-2110 MHz and 2165-2200 MHz bands, i.e., the International Table is updated."
More information is available in the Memorandum Opinion and Order - (ASCI text file (da992743.txt or Adobe Acrobat PDF file (da992743.pdf). Also see Appendices (Adobe Acrobat PDF files) da992743a.pdf, da992743b.pdf and da992743c.pdf.
- OTHER Items of Interest
>>>>Next January 10 - Issue 196
Return to The RF Page @
www.transmitter.com
Last modified January 9, 2000 by Doug Lung dlung@transmitter.com
Copyright © 2000 H. Douglas Lung