The Myth of Radio Spectrum Interference

Selanit writes "Just came across a fascinating article on Salon about a technologist who claims that there is no such thing as "interference" in the radio spectrum. He argues that interference is a symptom of inadequate equipment, not a fact of nature, and that with improved transceivers we could open the spectrum up to high-quality broadcasts by anyone. Reference is made to the GNU Radio Project. Neat stuff." We've posted other stories about this. I wonder if the "color" meme will catch on.

Comments

Re:The article is crap

[W32.Klez.A]

" This guy looks like a CS grad or (oh horrors) a digital designer. I would really love to see his credentials."

David Reed is many things, but crackpot is not one of them. He was a professor of computer science at MIT, then chief scientist at Software Arts during its VisiCalc days, and then the chief scientist at Lotus during its 1-2-3 days. But he is probably best known as a coauthor of the paper that got the Internet's architecture right: "End-to-End Arguments in System Design."

thank you for reading the article.

Re:complete bunk

[coult]

I have a Ph.D. in applied mathematics and am an expert in numerical methods for wave propagation, so I do know something about waves. Yes, one can imagine a different technology such as directional antennae or spead-spectrum, but how much more complex do your receivers have to be?

Clearly there is no such thing as limitless bandwidth; Shannon's theory tells us there is maximum amount of information that can be transmitted over any one channel, and simple physics tells us that there are a limited number of channels, no matter how you slice it.

Someone hand this guy a physics book, stat!

[Hal-9001]

I can't even begin to discuss all the things that are wrong with Reed's theories as described in the article, but I'll address some howlers.

"Photons, whether they are light photons, radio photons, or gamma-ray photons, simply do not interfere with one another," he explains. "They pass through one another."

There are some very commonplace phenomena, such as the colors on a soap bubble or oil slick, which are the manifestation of interference of light. There are more fundamental experiments that can be done with lasers or radio waves to demonstrate interference.

Reed uses the example of a pinhole camera, or camera obscura: If a room is sealed against light except for one pinhole, an image of the outside will be projected against the opposite wall. "If photons interfered with one another as they squeezed through that tiny hole, we wouldn't get a clear image on that back wall," Reed says.

Actually, if you do the experiment, there is a specific pinhole size at which you get the best image. Make the pinhole any smaller and the image starts getting blurrier because of diffraction effects which, loosely speaking, are due to the photons interfering with each other.

If you whine that it's completely counterintuitive that a wave could squeeze through a pinhole and "reorganize" itself on the other side, Reed nods happily and then piles on: "If photons can pass through one another, then they aren't actually occupying space at all, since the definition of 'occupying' is 'displacing.' So, yes, it's counterintuitive. It's quantum mechanics."

From his misunderstandings of the nature of light so far, it's impossible for him to have any real understanding of the quantum nature of light. He wouldn't know Schrodinger's equation if it walked up to him and smacked him upside the head, seeing as how Schrodinger's equation is a wave equation and predicts all sorts of interference phenomena.

The most fundamental problem is that he admits the notion of frequency, which is intrinsicly tied to the wave nature of light and radio. If he admits the wave nature of light, then he also has to admit interference of light as a natural phenomenon and not as a detection artifact, at which point all of his theories crumble.