ORLANDO, FLA.—I’ve been covering IEEE Broadcast Technology Symposiums for many years. The first BTS was 65 years ago and while I’ve only been attending the sessions for a fraction of that time, I’ve seen the annual event evolve. The first meetings I attended were held at the Hotel Washington in Washington, D.C.
Over the last 20 years, the focus of the Symposium has shifted from research papers like those in the IEEE Transactions on Broadcasting loaded with simulations and formulas towards practical solutions and technology for today’s broadcast engineers.
The Symposium now moves around the country—in recent years it’s been held in San Diego and San Antonio; in October, it was held in Orlando while next year, it will take place in Hartford, Conn. The changes were made to enable broadcast engineers to attend the sessions, keep it affordable, and make sessions more accessible to broadcast engineers who may not be designing antennas and transmitters, but who must make the right decisions on how to deploy and maintain them.
I’m surprised and a bit discouraged more broadcast engineers don’t take advantage of the BTS. Not only is the three-day event one of the best places to learn about new technology and FCC technical regulations, it provides a great opportunity to talk to experts one-on-one. You won’t find opportunities like these at larger events.
The symposium began early with an optional engineer’s tour of NASA’s Kennedy Space Center, which provided an inside look at the technology and culture at NASA. The Orlando Symposium started early with an optional, private tour of NASA’s Kennedy Space Center led by Jon Cowart. He started working at NASA as a project engineer for Shuttle Atlantis in 1987 and is now the NASA partner manager working with Space-X on the Commercial Crew Integrated Capability initiative. This engineers’ tour of NASA provided an inside look at not only the technology, but the NASA culture and the important role NASA plays. Those who missed the tour got a glimpse of Cowart’s passion for space flight and discovery during his keynote speech at the BTS/AFCCE lunch.
This month I’ll highlight some of the interesting sessions and discussions you missed if you didn’t attend.
REPACKING
The presentation “TV Repack: Post-Auction Transition Procedures” by Joe Davis of Chesapeake RF Consultants, answered many of the questions I’ve been getting from station engineers about repacking.
One question is how a station’s coverage might change. Stations moving to a new channel can file for an expedited grant of a construction permit without the need for an interference study if they can demonstrate the facility on the new channel will serve greater than 95 percent of the reference population and not extend the contour. A slight contour extension of up to 1 percent is okay if needed to achieve the new assignment or to address a loss area on the new channel. New interference to any other station must not exceed the 0.5-percent de minimis level, and the antenna pattern must closely conform to the new assignment.
If the newly assigned repack facilities cannot be constructed for reasons beyond the station’s control, it may be given priority treatment. Such stations can select alternate channels and will be able to extend their contour over 1 percent, provided new interference to other stations is limited to 0.5 percent. “Non-priority” stations changing channels will have an opportunity, after “Priority” stations, to increase coverage more than 1 percent, again with the 0.5-percent interference limit, under the usual processing guidelines.
Finally, after the repacked stations are taken care of and the FCC lifts the freeze on coverage expansion, stations that aren’t changing channels will be able to extend their contour. Stations that get repacked into the wireless “600 MHz” band are unlikely to be able to get any contour extension.
Davis outlined concerns about the process, noting that the limit of 1-percent contour extension will be a problem for stations with directional antennas, especially directional panel antennas, since their pattern changes with frequency. He showed an example where a 1,000 kW station could end up having its ERP dropped to 270 kW to avoid a greater than 1-percent contour extension. Stations already at 1,000 kW won’t be able to increase power if they have to move to a higher channel. This will result in a loss of coverage after adjusting for the dipole factor.
Davis’ presentation is not in the IEEE Symposium proceedings, but I hope he’ll make it available on the Chesapeake RF Consultant’s website www.rf-consultants. com at some point.
ATSC 3.0
The Thursday morning session was devoted to ATSC 3.0, and the overview from Skip Pizzi of NAB answered many of the questions I’m hearing from broadcasters about ATSC 3.0.
It was followed by detailed presentations on four of the “layers” of ATSC 3.0. Luke Fay, from Sony, covered the Physical Layer; Yongkwon Lim, with Samsung, outlined the Management and Protocols Layer; Madeline Noland, consultant representing LG Electronics, discussed the applications and presentations layer; Seton Droppers from PBS provided an overview of the security layer; and Peter Sockett from Capital Broadcasting presented “Advanced Emergency Alerting.”
These presentations did a good job describing the ATSC 3.0 framework, the options available, and how they fit into the overall standard. I’ll delve into them in detail in future columns. Luke Fay’s presentation is available in the Symposium proceedings. The ATSC 3.0 physical layer is described in two candidate standards now available on the ATSC website (http://atsc.org/): A/321 Part 1: System Discovery and Signaling and A/322: Physical Layer Protocol.
RF PROPAGATION
Both the repacking and ATSC 3.0 transition will require use of propagation software to determine coverage and interference. While several propagation models are available, the one most widely used is Longley-Rice, also known as the ITS Irregular Terrain Model (ITM), Version 1.22.
This model was last updated in 1984, although documentation and source code have been updated since then, with the last update to the ITMDLL.cpp C++ source code in June 2007. While there are more recent propagation models available, the availability of source code and zero licensing cost of ITM have kept it the standard for coverage and interference studies over terrain.
Sid Shumate with Givens & Bell in Haymarket, Va., has been working on improving the accuracy of the ITM code and incorporating propagation models from ITU P.1546 and his own research. At the Symposium, Shumate provided details on his latest work in the session “Improving the 2-Ray Calculation in Longley-Rice.” In his improved model, Shumate takes into account the effect on losses from non-flat reflection points; ITM does not consider spreading loss from non-flat surfaces. He also provides a simple method for calculating the total distance traveled by the reflected ray.
Summarizing his presentation, he concluded, “The diffraction effects at a knifeedge obstruction can now be seen to be short-distance effects. Because of the rapid fade due to circular spreading, the signal reflected and/or retransmitted from a rounded knife edge tip has a short range. As a result, it is not the primary source of radio reception at significant distances beyond an obstacle.”
While his presentation was not included in the proceedings, you can email him at sid@givensbell.com for a copy of the paper, slides and worksheets.
OTHER NUGGETS
I’ll cover more of what I learned at the 2015 IEEE Broadcast Symposium in future articles, but here are a few nuggets of information I found particularly interesting.
In Davis’s presentation, he said the FCC will release a version of TVStudy that would allow interference analysis. Anyone who has tried to use TVStudy for interference analysis knows that extracting the data needed for the analysis is difficult and the results, at least in my experience, do not match those from the current FCC TV application processing software, tv_process.
The new version of TVStudy will make it easier for broadcast engineers to conduct interference studies, something that will be critical in the short filing windows in the repacking.
Dielectric’s Keith Pelletier’s paper on “RF and Antenna Transition Strategies” deserves coverage in its own column. Resources to replace or retune transmission lines will be limited during the 36 months or less allowed for channel changes. One tidbit I found useful was there is a good chance existing transmission line can be reused on the new channel, even if the section length, which is selected to minimize the impact of flange reflections, is not optimum. He said this is especially true if a solid-state transmitter is used, as they are not as sensitive to reflections as IOT or other tube transmitters.
Tim Laud with Zenith Electronics presented “First Field Testing of Proposed ATSC 3.0 Physical Layer Technologies.” I’ll cover ATSC 3.0 field testing in future columns, but it is worth noting that one of the test locations was in the basement of a downtown office building in Cleveland. On a spectrum analyzer, LG’s Futurecast signal was indistinguishable from the noise floor, but the television showed clean reception of the most robust mode. As expected, no ATSC 1.0 reception was possible.
After a scheduled paper was pulled from the Symposium, Merrill Weiss overnight created and delivered a presentation on implementation of SFNs and STL links in ATSC 3.0. As expected, the flexibility of ATSC 3.0 and its use of IP is going to require a different approach to formatting the data sent to transmitters, even if existing infrastructure (IP via directly or encapsulated into ASI packets via fiber, microwave or satellite) is used. This is a critical topic I’ll cover in more detail in future columns.
If you’re a member of IEEE, I hope this overview will encourage you to attend next year’s Symposium in Hartford. If you are not a member of the IEEE Broadcast Technology Society, now may be the time to join! You can learn more about the IEEE Broadcast Technology Society, next year’s Symposium, and how to join at www.ieee.org.
Comments are welcome! E-mail me atdlung@transmitter.com.
