RF Shorts – May 18, 2012

1WTC Height Debate Continues
Carl Bialik has more on the debate over One World Trade Center's spire should be considered an antenna, in which case it wouldn't be considered as part of the building height, disqualifying 1WTC as the western hemisphere's tallest building, or whether it should be considered part of the architecture, making in which case, when completed it would qualify. Last week I reported on concerns that removing the shroud from the spire would disqualify it.

In another Wall Street Journal article last week, Steps Unclear in Builders' Race to Top Bialik says "Now the height of One World Trade Center is up in the air, since an antenna, unlike a spire, isn't ordinarily counted toward a building's height, in part because it can be moved."

Last week's news reports appear to count the 408-foot mast as an antenna, if it doesn't have a shell around it, and as a spire, if it does. This argument doesn't make sense to me, as the mast itself would not be an antenna – the antennas would be attached to it, just as they are on the masts on the Empire State Building and on Willis (formerly Sears) Tower. In the competition for the height of the tallest building, the mast and antennas on Willis Tower do not count.

It may not turn out to be a big issue – spokesman for the Council on Tall Buildings and Urban Habitat in Chicago Kevin Brass said last Thursday, "Ultimately the final height is not determined until a building is complete."

Wednesday Observer.com reporter Matt Chaban wrote The Neverending Story – Get to the Point: If Anyone Can Save 1 WTC's Symbolic Spire, It Is the Dursts—They Snuck Onto the Skyline Before. He says, "The problem is that the council does not recognize antennae, flagpoles, signage or other superfluous structures as contributing to the height of the building. That is why the Willis Tower, 1,451 feet, ranks eighth tallest in the world, even though two broadcasting arrays bring its total height to 1,729 feet, the second tallest in the world behind the Burj Khalifa."

I agree with Chaban's comment, "This seems absolutely backwards—why encourage 'spires,' useless poles with a glimmer of design intent, while forgoing actual, functional structures like antenna and signage. Whatever happened to form follows function?" Kevin Bass replied, "It's a practical concern. What is to stop someone from just adding on a taller and taller antenna?" Chaban notes that the Dursts added what he describes as "a white toothpick" to their One Bryant Park building to push its height from 945 feet to 1,200 feet, making it New York's second tallest building at the time.

Dutch TV Tower Rebuilding Completed
BroadbandTVNews.com reported on May 13 Rebuilding of Dutch TV tower finishes today. The web site has a video from a helicopter flying around the antenna mast. Robert Briel reports that "For the past two weeks, construction work on the TV tower, which was destroyed by fire last year, has been going on using a helicopter to put the long antenna mast in place."

EDN Article Explains Envelope-tracking Power Amplifiers
An EDN.com article Understand and characterize envelope-tracking power amplifiers provides detail on the challenges involved in building envelope-tracking amplifiers.

In the article, Gerard Wimpenny from Nujira Ltd writes, "The system-efficiency benefit of operating a power amplifier in envelope-tracking mode is well-known. However, it also offers other useful system benefits, such as increased output power, improved operation into mismatched loads, and insensitivity to temperature variations." These benefits do not come easily. He explains, "In contrast to fixed-supply power amplifiers, the performance of an envelope-tracking power amplifier requires the gathering of substantially more data to predict system performance and the use of a test environment that allows sweeping of the supply voltage and the input power. A key aspect is the definition of the shaping table, which defines the relationship between supply voltage and RF power. Once you define the shaping function, you can directly measure efficiency and linearity using an appropriate system-characterization bench."

Thomson Broadcast uses envelope-tracking to achieve high efficiency in their Futhura solid-state transmitter.

Doug Lung is one of America's foremost authorities on broadcast RF technology. He has been with NBC since 1985 and is currently vice president of broadcast technology for NBC/Telemundo stations.