RF Shorts for Aug. 22, 2013

1936: The Dawn of Television in the U.K.
Jon Excell has an interesting article, with pictures, of This week in 1936 – the dawn of TV broadcasting on The Engineer website. Excell writes, “Today, London’s Alexandra Palace is known around the world as the birthplace of television broadcasting— arguably one of the most disruptive innovations of the 20th Century. But back in 1936, few could have anticipated the way in which television would come to dominate public life. And following a visit to the London Television station in August of that year, the Engineer reported on the technology in a characteristically measured tone. The full report can be read here.

The story and pictures show how far TV has come in the past 77 years! I wonder what TV broadcasting will look like 77 years from now, assuming it is still around!

Roxborough Antenna Farm Radio Signals Creeping Into Nearby Homes
Alan Jaffe says Roxborough's antenna farm has some neighbors hearing 'creepy' (but safe) voices in his article and video on Newsworks.org. Engineers know that dissimilar metals can act as rectifiers and lead to radio signals being picked up by downspouts or even metal fillings. In his report on strange happenings near Philadelphia's main antenna farm, Jaffe says, “At their home on Harmon Road in Roxborough, Pa., Shane and Jocelyn Brody hear voices through the pipes in the basement. In their backyard, Mexican melodies emanate from their neighbor's metal fence. Occasionally, they pick up what must sound like heavenly messengers—but is actually Christian programming that they receive through their rain spout.”

Jaffe deserves credit for explaining the cause of the odd sounds and notes that consulting engineer firm Carl T. Jones Corporation did a study for a nearby charter school and found the towers were not hazardous.

It is not surprising that newer homes with plastic pipes do not experience the same problem. What isn't mentioned in the article is that the spurious signals generated by the corroded metal connections could be causing widespread interference to cell phone base stations and other sensitive receivers in the area. Not too long ago a cellular company asked me about interference they had traced to the Roxborough antenna farm. From the spectrum analyzer plots they provided it looked like a case of PIM—passive intermodulation. While most site operators take great effort to minimize PIM, tracking down and fixing PIM from private homes near tower sites is going to be much more difficult!

Comments and RF related news items are welcome. Email me at dlung@transmitter.com.

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.