TV Technology - January 7, 2009 - (Page 22)

FEATURES uncompressed, very large, and slow to load. Use a graphic program to convert them to PNG and then modify the image filename in the kml file to match for faster map response. After loading the file in Google Earth, zoom in to see how terrain and building impact signal strength. Remember that the signal strength is based on an antenna 4 meters (or whatever height was specified in SPLAT) above the terrain/foliage/buildings. The zoomed area of the Google Earth map with WNJU-DT coverage shows the impact of buildings in lower Manhattan on the signal from the West Orange, N.J. transmitter site based on an antenna 4 meters above terrain (see Fig. 1). When viewing this map, keep in mind that the cells are three seconds on a side. This means there could be significant variation inside the cell— from 4 meters above the rooftop of a building to the street below. The color scale for the map ranges from dark orange at 98 dBμV/m through yellow to dark green at 68 dBμV/m and then cyan at 58 dBμV/m and ends up at violet for 41 dBμV/m. The underlying color of the Google Earth map has some impact on the signal strength overlay color. The www.xmtr.com/splat Web site has links to the files used to create this map and the home of SPLAT at John Magliacane’s Web site. RF TECHNOLOGY Doug Lung DTV Transition Survival Guide hile it’s probably too late to make any major changes before the analog shutoff next month, there are steps broadcasters can take to avoid unpleasant surprises. W nels. While some systems carry the broadcaster’s PSIP data, many don’t. This will make it hard for subscribers to receiving its DTV signal. Viewers that are getting good reception from a station’s UHF DTV channel may not have MAKE SURE YOUR SIGNAL DOESN’T DISAPPEAR In most markets, more viewers watch TV over cable or satellite than over-the-air. While DirecTV, Dish and the larger cable MSOs are already taking feeds from over-the-air DTV or fiber to feed their headends, there is a good chance many master antenna systems in apartment buildings and condominiums have not prepared for the shutdown. Because viewers in these buildings have their TV sets hooked up to an outlet in the wall, they may assume that they are getting cable TV and feel they are OK even if they see snow during analog “soft shutdowns.” In older buildings, it’s possible the company that did the original installation is no longer in business. Someone, however, has to maintain the system. If you are lucky, you may be able to find someone responsible for several systems. Don’t be surprised if they are working for a company selling telephone systems or DBS subscriptions. Stations changing DTV channels after Feb. 17 have a special challenge. I suspect many stations will drop off some systems for a few days until someone changes the receiver tuning. The outage could be worse if the new channel can’t be received due to a weaker signal, the wrong antenna (using a UHF antenna on VHF for example) or inter, ference. The FCC recently allowed a station to broadcast on two DTV channels simultaneously so it could transition cable and satellite companies to its new channel before shutting off its outof-core pre-transition DTV channel. While my limited tests showed no problems on current DTV sets and older converter boxes, a reader did a more extensive test with newer converter boxes and found some had problems with the same stream on two different channels. Simulcasting isn’t an option for stations moving back to their analog channel post-transition, but it may be worth sacrificing some analog airtime to test reception at headends now. If there are problems, it will give the cable or satellite company time to fix it. Most DTV sets sold include ClearQAM tuners that provide reception of unencrypted digital cable chan- Courtesy of Google Earth Fig. 1: A Google Earth map with WNJU-DT coverage shows the impact of buildings in lower Manhattan on the signal from the West Orange, N.J. transmitter site. find your channel on sets not hooked up to a set-top box. Try hooking a DTV set directly to a cable outlet. Punch in your major/minor channel number. See what happens. If nothing shows up, do a channel scan see where your station is located. There is little time to fix the problem, but it is worth the effort, especially if cable subscribers can punch in your competitors’ major-minor channel number and see its station. Most cable operators are willing to work with broadcasters on PSIP issues. FCC rules Section 74.640 requires systems with 750 MHz or more activated channel capacity carry broadcasters’ PSIP according to the ATSC A/65 standard, available at www.atsc.org/standards/. It may be difficult to find time to locate and contact every MVPD (multichannel video programming distributor) and master antenna system to make sure they are ready for the shutdown. If that’s the case, prioritize MVPDs based on the number of subscribers. Enlist the help of employees and other viewers to find out what apartment buildings may have problems. Station giveaways (hats, T-shirts, coffee mugs, etc.) might help in recruiting viewer volunteers. KNOW YOUR DTV COVERAGE Sometimes viewers receiving a station’s analog channel have problems as much luck if it switches to a VHF DTV channel post-transition. Alternatively, some viewers that aren’t getting a station’s UHF DTV signal may find they are able to get the post-transition VHF DTV signal, if they have the right antenna and re-scan their DTV set or converter box. Knowing what your DTV coverage looks like now and what it will look like on Feb. 18 is important. Coverage can be determined using computer propagation models or by field measurements. John Magliacane’s SPLAT software makes it easy to calculate DTV coverage using the Longley-Rice propagation model and the shuttle radar terrain mapping mission three second elevation data. (See my past articles on SPLAT and my SPLAT resource page at www.xmtr.com/splat for details on installing and running SPLAT.) A computer model is only as accurate as the input data. Use the most accurate antenna azimuth and elevation pattern data available, including tower scattering if possible. SRTM elevation data includes buildings and trees present during the shuttle mission in February 2000. When using SRTM topographic data, you may want to use a lower receive antenna height to obtain more realistic results. SPLAT now provides the ability to save the study as a PPM image and a Google Earth kml file. PPM images are Paul Sokoloff (WCAU) adjusts antenna for signal measurements. Field measurements provide a way to find major differences between calculated and actual antenna performance. One procedure for field strength measurements is outlined in the FCC rules. Gary Sgrignoli, founder of Sgrignoli Consulting, details procedures for DTV field measurements in his VSB measurements seminar. Many stations won’t have the time, equipment or money to do detailed measurements or to hire someone who can. I’ve come up with a simpler, faster, easier method that’s sufficient to show any major coverage abnormality. My method uses an antenna at 12 to 15 feet above ground. At 12 feet, a light stand provides sufficient stability in light winds. For greater heights, a drive-over mount like the one shown 22 January 7, 2009 • TV Technology • www.tvtechnology.com http://www.xmtr.com/splat http://www.atsc.org/standards/ http://www.xmtr.com/splat http://www.tvtechnology.com

Table of Contents Feed for the Digital Edition of TV Technology - January 7, 2009

TV Technology - January 7, 2009 NFL Enters a New Dimension Mobile DTV Looms Large in 2009 Contents A ‘Flexible Framework’ Doing More With Less ‘X’tra-Streamlined Finish Line in Sight for BAS Transition Ahead of the Relocation Curve DTV Transition Survival Guide ENG and the Lines of Communication DTV Transition Survival Guide Who Do We Really Work For? Obama to Expand Internet Access The Wizard Takes a Holiday The Solid-State Disk Revival To Light the Ear... or Not Hulu Gets It Right—the First Time User Reports—Video Servers & Recording/Controllers Reference Guide Product Showcase Classifieds Marketplace TV Tech Business

TV Technology - January 7, 2009

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