It Came Out of the Sky -- A Myth Is as Good as a Mile



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Home Articles STARK REALITIES About This Site My PGP Public Key


After Hours Ordinary Hero A Season in Methven Our Host Send Me Mail


Home Articles STARK REALITIES About This Site My PGP Public Key


After Hours Ordinary Hero A Season in Methven Our Host Send Me Mail


Home Articles STARK REALITIES About This Site My PGP Public Key


After Hours Ordinary Hero A Season in Methven Our Host Send Me Mail


Home Articles STARK REALITIES About This Site My PGP Public Key


After Hours Ordinary Hero A Season in Methven Our Host Send Me Mail


Home Articles STARK REALITIES About This Site My PGP Public Key


After Hours Ordinary Hero A Season in Methven Our Host Send Me Mail


Home Articles STARK REALITIES About This Site My PGP Public Key


After Hours Ordinary Hero A Season in Methven Our Host Send Me Mail


Home Articles STARK REALITIES About This Site

We had a pretty spectacular thunderstorm here in Mariposa last night. Even the coyote chorus was cowed into silence. The skies were filled with lightning and the rain thundered down in sheets.

By this morning, the tempest had passed, leaving in its wake air so crisp and winey that it made me want to bite into it, just to hear it crunch.

And that's a rarer occurance than you might think.

The thing is, city folks seem to have a persistent misconception about "clean, fresh country air." What they don't understand is that -- at least here in the Sierra foothills -- the atmosphere is thick with wood smoke more often than not.

This is extremely arid country in Summer -- the average humidity index is well down into single digits -- and therefor the oak and evergreen forests that cover the Sierras are tinder-dry.

Huge sections of those woods haven't seen fire in fifty years or more, so, when they do burn, it's as a crown-fire holocaust that ravages and destroys, instead of cleaning and renewing. So tourists' carelessly-discarded cigarette butts, lightning strikes or cars' hot exhaust systems regularly spark conflagrations that are brought under control only through the efforts of literally thousands of firefighters.

Consequently, in the dry season, the atmosphere in Mariposa is often smoke-filled -- and our air quality doesn't improve much in the rainy season, either.

That's because 90% of the county's residents heat their homes with wood stoves. They contribute a lot of smoke, both directly from their fuel and indirectly, from the ubiquitous piles of burning brush and branches we accumulate during the dry season.

Then there's the dust and the exhaust from the endless stream of smog-belching tour buses and..

Well, you get the idea.

There are a lot of misconceptions about wireless technologies, as well. Take, for example, the belief that 802.11b signals have an inherent maximum reach of 100 meters. The fact is that 100 meters is more of a minimum range than a maximum one.

I Can See for Miles

As wireless security maven Peter Shipley mentioned in this column a few weeks ago, he's successfully managed to login to quite a number of wireless LANs from as much as twenty miles away -- literally from over the horizon. Shipley accomplishs his long-distance logins with the aid of a signal amplifier and a custom-designed parabolic antenna, but it's easily possible to extend the range of 802.11b connectivity with much lower-cost solutions.

In fact, in about an hour, a moderately-handy person can construct a Yagi-Uda array (a highly directional antenna named after Hidetsugu Yagi, the electrical engineer who invented it, and Shintaro Uda, who later refined Yagi's design) that will add up to 15dB of gain to a Wi-Fi network, using nothing more than an empty Pringles(TM) can, around five bucks worth of other parts and such specialized tools as a glue gun, a hacksaw and a soldering gun. Properly aimed, a pair of those boys can add ten miles or more to the range of an 802.11b net, at a heckuvva lot lower price than, say, a T1 or DSL connection.

The same general design should work equally well for 802.11a -- the next evolution in unlicensed wireless networking -- when gear that supports that much-speedier 5GHz technology spec begins rolling out. You'll only have to adjust the length and spacing of the array elements in order to stretch the range of what the marketeers may well dub "Wi-Hi" by a a couple of orders of magnitude.

Of course, when adding a roll-your-own antenna, an amplifier or any combination of the two to an 802.11 network, you'll want to make sure you're in compliance with Section 247 of Part 15 of the FCC's Title 47. (Which is to say, the rules for operating what the Feds call "intentional radiators" in the unlicensed portion of the radio spectrum -- including the 2.4GHz band where Wi-Fi lives.)

The Feds are pretty intent on keeping your extended-range wireless LAN's signal from interfering with your neighbor's cordless telephone, you see. And they can get downright nasty about it, if your neighbor happens to be savvy enough to file a complaint, so it behooves you to have your regulatory ducks aligned, just in case your friendly, neighborhood FCC inspector happens to pay you a courtesy call.

You won't have to worry about whether your Bluetooth headphones will interfere with your 802.11b LAN, though. As it turns out, that just doesn't happen in the real world.

Permit me to explain.

Am I Blue?

Back in early September, I attended DEMOmobile 2001, an IDG Executive Forum that was held at the Torrey Pines Hilton in San Diego. The Demo shows are just the kind of event I look forward to attending: tightly-focused, well-choreographed and with the number of exhibitors purposely kept small enough that I can get something more detailed than the "elevator pitch" from each of them.

There were just 31 demo-ers, all told, and one of them was Pico Communications, (which was there to demonstrate its Bluetooth Internet Access Point.) When I dropped by to talk to the Pico folks about their product, I mentioned Peter Shipley's concern about Bluetooth data streams interfering with Wi-Fi, cordless phones and other residents of the 2.4GHz airwaves to Lung Yeh, the company's Ph.D. President and CEO.

"It doesn't happen," he said. "Maybe if you have both a Bluetooth and an 802.11 card in the same laptop. Otherwise, no."

"Well," I told him, "intellectually speaking, I'm from Missouri."

He grinned.

"You want a demonstration?" he asked.

"As a matter of fact, I do."

"No problem," he said. "Tell me what you want to test and how you want to test it. We'll set it up for you."

I thought about it for a while before I made my way back to the Pico Communications booth.

"Here's what I want you to do," I told Yeh. "Set up two laptops: one with a Bluetooth PCCARD, the other with a Wi-Fi card. Then point them both at a streaming media site out on the Internet -- let's make it a music video site, so that we're pulling high-density, continuous data down to both computers. Then have each machine play a different video and let's see what happens."

Yeh nodded.

"Good test," he said.

So, while I watched, Yeh and his techs set up the two computers, just as I'd specified, and started playing the two videos -- both of which I selected -- as I observed and listened closely.

There was no interference audible or visible on either machine. None. This, despite the fact that Pico's Bluetooth access point sat squarely between the 802.11b box and its own access point -- a setup that should have guaranteed interference, if there were any to be had.

That wasn't quite convincing enough a demonstration for Dr. Yeh's tastes, so he then repositioned the two computers in such a way that their network cards' respective antennae were just over an inch apart.

I could still discern no interference.

"Satisfied?" he asked.

I nodded.

"Yup. You've got me convinced."

Yeh's demonstration had laid my Missouri to rest -- and it was sleeping peacefully enough that I promised him I'd explode that little misconception before the very eyes of developerWorks' readers. And credit him and his crew for providing the evidence, to boot.

My hat's off to you, Dr. Yeh.

You rule.

Bring it on Home

So, how did the Bluetooth interference shibboleth -- easily disproved as it is -- wind up as such a widely-credited item of common knowledge?

I suspect it began life honestly enough, as a speculation based on the standard's own technical specification combined with network professionals' inherent respect for Murphy's Law. And, because for a long while, there just wasn't any Bluetooth equipment available to anyone but developers, the longer it remained untested, the more that speculation became an article of faith. Eventually, it was elevated to the status of dogma by the trade press and its endless appetite for sensation and poor fact-checking habits.

Kinda makes you wonder how long it'll take the truth finally to replace the urban legend, doesn't it?

Like the "clean, fresh country air" truism, such bits of common knowledge, repeated often enough, tend to take on a life of their own. Thus "everybody" -- except the folks who actually work with the stuff -- knows that 802.11b LANs have a maximum range of 300 meters at 11Mbps and that Bluetooth will interfere with 802.11b networks.

And those bromides are every bit as accurate as the one about how quiet it is out here in the country. Of course, if you overlook the chain saws and riding lawnmowers, the log splitters and ATVs, the pickup trucks and the tractors, I'd suppose you could make a case that it really is that silent..

..except for the coyotes and foxes, the woodpeckers and jays, the crickets and cicadas, the barking dogs and the howling of the wind through the endless acres of oaks and pines. And so on.

But, heck, all that goes without saying.

And everybody knows it.

 
Resources:

My developerWorks column about Peter Shipley's "war-driving" research

The full transcript of my interview with Shipley

Techtarget's Whatis definition of a Yagi-Uda array

Rob Flickenger's excellent article on how to build a Pringles-can Yagi

L Victor Marks' comparison of (among other things) 802.11a and 802.11b

1999 IEEE 802.11 standards documents (all in PDF format)

Part 15.247 of Title 47 - antenna specs for "intentional radiators"

Brent A. Miller's survey of likely Bluetooth applications

IEEE 802.15 WPAN Task Group 2 (TG2)'s page on 802.11b/Bluetooth Coexistence Mechanisms

DEMOmobile's Web site

Pico Communications' Web site

. . .

A somewhat different version of this work was first published by IBM developerWorks at
http://www.ibm.com/developerWorks/

(Copyright© 2001 by Thom Stark--all rights reserved)