There Is No Cat

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Thursday, June 10, 2004

Panacea or same old same old?

Doc Searls brings my attention to an interesting development in antennas: a man in Rhode Island, Rob Vincent, is claiming to have come up with a novel and effective way to shorten antennas, which have to be monstrously large at low frequencies. Rob Vincent was a frustrated ham operator with an interest in the 160 meter band, just above the top end of the AM (medium wave) broadcast band. AM stations typically load up their towers to get maximum signal. A station at 1500 kHz, for example, would need a tower about 50 meters high (say, 160 feet) to resonate at a quarter of the wavelength of the transmitter signal. Few hams operating on 160 meters can afford to erect a tower 40 meters high to get that quarter wavelength. In fact, generally speaking, the antenna of choice for DXers interested in medium wave and the low end of shortwave (up to about 5000 kHz) is a long wire about ten feet above the ground, known as a Beverage antenna after the man who invented it in the early 20th century, Harold Beverage. At my last house, I erected an antenna that was long enough to start to show the characteristics of a Beverage antenna, and at the new house I've erected a similar antenna that's even longer, about 90 meters long, that shows promise. Not everyone has the ability to put up long or tall antennas, however, so anything that promises to shorten antenna length and mediumwave and shortwave frequencies would be of great interest.

But when I read a little further, I became a little skeptical. The New York Times article about the antennas mentions the use of loading coils as being crucial.

Loading coils?

Antennas based on loading coils have been sold for decades. Commercial antennas like the Alpha Delta DX Sloper and the Eavesdropper Sloper use loading coils to provide short antennas for installation in middling-sized suburban yards. I've been a shortwave listener for 27 years, and I don't remember there ever being a time when loading coils weren't a prominent feature on certain well-considered antennas. This is nothing new, and certainly nothing patentable. The University of Rhode Island press release about the antenna calls it a "distributed-load monopole antenna". Heck, that sounds like the broomstick antenna long pushed by Radio Havana's Arnie Coro, which gains length by winding wire around a dowel or a PVC pipe so that you get lots of wire into a small space.

The Times article says that Mr. Vincent's design improves on conventional designs in several ways. That may be so. I certainly look forward to reading the patent when it's published to see if this is anything more sophisticated than what's described in the article. Because given that the Times only compares Vincent's antenna to broadcast towers, I'm not sure if "conventional designs" refers to those towers, or to the longstanding practices of the type shown in the sloper antennas. There are certainly innovative and unique design approaches coming out in recent years for antennas. Fractal antennas were a surprise. The BLAST antenna arrays developed at Bell Labs show great promise at very short wavelengths such as those used by cell phones. (Neither of these designs work at the frequencies of interest to me and to Mr. Vincent, by the way). The article quotes someone at the ARRL, the organization of amateur radio operators. He seems skeptical. I share that skepticism. Maybe there's something new here. Or maybe it's just a reinvention of the wheel. (Not that that's stopped the patent office in recent years....)

Postscript (added 10:49 pm): I ran this by a friend of mine who is a longstanding engineer, shortwave listener, and ham, and who writes a technical column for the NASWA Journal, the monthly publication of the North American Shortwave Association. (Disclaimer: I am on the board of NASWA, and help publish the Journal every month.) He points out that the Times article talks about an antenna that melted when fed with 100 watts. He says, "Antennas melt because they are inefficient and change RF energy into heat. A truly efficient antenna would not melt." He's been in to radio for many more years than me, and points out that loading coils have been around since the 1920s. Doc's suggestion that these antennas might replace AM broadcast towers seems unlikely to me; cooling the heat generated by such an antenna would likely take more money than just building the full tower in the first place.

Posted at 10:19 PM


Note: I’m tired of clearing the spam from my comments, so comments are no longer accepted.

Read the article in EETimes It has a bit more info than the Times and may make abit more sense. I am also a "doubting Thomas" but we shall see.

Posted by Lochlin Page at 12:49 PM, June 17, 2004 [Link]


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"You see, wire telegraph is a kind of a very, very long cat. You pull his tail in New York and his head is meowing in Los Angeles. Do you understand this? And radio operates exactly the same way: you send signals here, they receive them there. The only difference is that there is no cat."

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