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.

NOTICE You may have noticed that near the end of the month, the RF Current page had grown rather large. Starting this month, each issue will have its own HTML page. This should make it faster to load, easier to search and make it a little easier for me to edit. I now have access to an Excite search engine. As soon as I can figure it out, I plan to have all issues search able from the new back-issues list.

<<< Back to April 12 - Issue 161

April 19, 1999 - Issue 162 Final Edition

DTV - Philadelphia ATSC Reception Tests Demonstrate Indoor Antenna Problems (Apr. 19)
A hot topic among RF engineers at NAB this year was whether the 8VSB modulation selected by the ATSC and the FCC for terrestrial digital broadcasting was robust enough to work in real world situations with indoor antennas. A simple study by Sinclair Broadcast Group that showed indoor reception of four DTV stations in Philadelphia was almost impossible fueled discussions.

Sinclair tested reception using four consumer DTV set-top boxes - two from Panasonic and one each from Sharp and Zenith. Outdoor reception using a yagi antenna was successful in all but one case. Indoor reception, using a Bow Tie Dipole, was unsuccessful in all but four out of thirty two situations. In those four circumstances at four locations, reception was intermittant. With only five locations studied, this is hardly a scientific study. It does, however, indicate a need for future study. Signal strength was not a limiting factor during these tests. Sinclair is planning additional tests, including a comparision with a COFDM DVB-T signal, in Baltimore Maryland later this year.

At the Objective: DTV session Sunday afternoon, the study was dismissed with a comment that the stations monitored were not operating at full power. In a session Tuesday, Robert Siedel reported successful indoor reception of WCBS's DTV signal in multipath prone New York City. Discussions with vendors in the exhibit area indicated the set top boxes tested were first generation designs and new circuitry performed much better. Others expressed concerns about the high peak to average ratio needed for COFDM transmission and the greater signal strength needed for COFDM reception.

For more information, see the Sinclair Broadcast Group Philadelphia ATSC Reception web page. For comparison of 8VSB and COFDM for terrestrial DTV transmission, see the Results Summary for Australian 7 MHz Laboratory Test of DVB-T and ATSC DTTB Modulation Systems and the ATSC Comments on the Report of the Australian DTTB Selection Panel.

TV - New TV RF Products at NAB 1999 (Apr. 19)
Most broadcast equipment manufacturers use the annual National Association of Broadcasters convention to announce new products. Inthe area of RF equipment, interest focused on the DTV buildout now underway. Several new transmitter, DTV encoder and related digital products were either introduced or enhanced this year. Products of particular interest will be covered in the RF Technology column in TV Technology. The list below lists product announcements available on the Internet:

Acrodyne
California Microwave (now Adaptive Broadband, aka MRC)(Links fixed May 2)
EMCEE
Harris
K-Tech Telecom
Lucent Digital Video
NDS
THOMCAST/COMARK/CDS
Zenith
MICROWAVE - COFDM For Terrestial Microwave News Gathering Displayed at NAB 1999 (Apr. 19)
For the past few years, digital transmission systems have been available for electronic news gathering. Most were limited to use on portable satellite uplinks outside the United States. With the loss of part of the broadcast auxiliary 2 GHz microwave band to mobile satellite services, the same spectrum squeeze that made the expense of digital transmission practical over international satellite links is now impacting terrestrial microwaves. For most stations, however, the real advantage of COFDM based digital microwave systems will be the ability to send video from moving vehicles and out of difficult locations where multipath is a problem.

California Microwave, NEC and Nucomm both had demonstrations showing video from moving vehicles. Tapes compared analog microwave signals with the COFDM signals. California Microwave and NEC had a vehicles driving around Las Vegas and under hotel entrances sending live video back to receive antennas near the Las Vegas Convention Center. Their performance was outstanding. No break-up was observed while viewing the live Las Vegas drive-around at the California Microwave booth. This technology should prove useful for following those pesky car chases in Los Angeles.

California Microwave (soon to be Adaptive Broadband) used a COFDM modulator and demodulator from NDS for its demonstrations. Nucomm used a COFDM modulator and demodulator from NEC but also had COFDM equipment from Sagem on display in their booth. More information on these demonstrations can be found in the following press releases:

No information on COFDM was available on the Nucomm web site when this was written.

DTV - Study Says DTV Must-Carry will "Disconnect" Local Phone Competition for Cable TV Systems (Apr. 13)
A study by Cahners In-Stat group found cable bandwidth would not be able to meet the requirements for carrying broadcasters' DTV signals and offering local phone service via cable. In the short term, up to 2001, the study did not see a bandwidth crunch, since digital signals will come primarily from the four major network affiliates and cable companies will be beginning to roll out local phone service. However, after 2002, Cahner's said "Digital must carry will cause a train wreck to local phone service." All commercial broadcasters are required to have a digital signal on the air by May 2002. This could mean up to 10 or more digital signals falling under Digital Must Carry regulations. The study said "If cable TV systems are forced to carry these additional digital signals they will not have the capacity to offer local phone service, and could lose up to $1.3 billion in revenue."

From the Cahners In-Stat Press Release announcing the study, it was not clear if the study considered the use of more complex digital modulation methods, which can place up to four broadcast DTV channels in the space occupied by one analog channel or the FCC simulcast requirements, which would eventually phase out the need to carry a separate analog signal once all programming had to be available on the broadcaster's digital channel.

DIGITAL TELEVISION STATION APPLICATIONS - See ap990415.txt for more information
Call (DT) Ch. Licensee Location ERP (kW) HAAT (m) Antenna
WUNC 20 Univ. of N. Carolina Columbia NC 543 489 Dielectric TFU-30GTH-R-04


DIGITAL TELEVISION STATION ACTIONS - See ac990415.txt for more information
Call (DT) Ch. Licensee Location ERP (kW) HAAT (m) Antenna
KUPX 29 Paxon Salt Lake Provo UT 60.3 Amended to 530 1171 Dielectric TUP-SP2-12-1 & TUP-SP1-4-1


OTHER Items of Interest

Next April 26 - Issue 163


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Last modified April 27, 1999 by Doug Lung dlung@transmitter.com
Copyright 1999 H. Douglas Lung