[CLUE-Tech] wireless problem

Sun Feb 15 09:34:37 MST 2004

This post is pure gold, and should be saved by everyone who has any 
interest in wireless interference.  I've been surveying microwave 
transmissions since 1993, and the problem is definitely getting worse.  
Biggest offenders are often government agencies.  I could tell you a 
very interesting horror story about an apartment i used to have near the 
Federal Center in Denver.

I got into surveying microwave and RF because sometimes health problems, 
especially in children, are directly linked to transmissions.  I have 
some case histories that definitely prove this out.  That said, the 
802.11 transmissions are such low power that they are not likely to 
affect health -- and that also means they are more vulnerable to 
interference from "bigger guns" in the neighborhood.

Anyway i think this laizzes-faire approach may be wrong, but we're stuck 
with it.  All of us who have concerns should be getting RF analyzing 
gear at any opportunity, because with that we will be able to help our 
neighbors and colleagues.

On Friday, February 13, 2004, at 09:17 PM, Nate Duehr wrote:

>
> Unfortunately 2.4 GHz low-power devices abound.  Baby monitors, 
> Cordless Phones, even your microwave oven's center frequency is around 
> 2.4 GHz (just happens to be the right frequency for warming water 
> molecules -- thus how the food gets cooked).  The bands used to be 
> licensed, but the FCC's latest "grand experiment" has been to open up 
> bands and let them become a free-for-all.  It has brought us great 
> gains in devices like 802.11b and 802.11g wireless cards but it also 
> comes with it the joy of interference.
>
> First a theory:
>
> From your description, I think you're struggling with a new broadbanded 
> 2.4 GHz transmitter in your neighborhood.  The only sure-fire way to 
> find it would be to do a site survey with a radio service monitor and a 
> spectrum analyzer.  However you might be able to pick up one of these 
> cheap $20 "find 802.11b signals" type gadgets... they're just a cheesy 
> 2.4 GHz receiver and a light, in many cases.  In your case, the cheaper 
> the better -- you don't want one with enough intelligence to tell the 
> difference between 802.11b signals and other transmitters.
>
> It could also be an 802.11g system if you live in close proximity to 
> your neighbors (apartments, multi-family "dwellings"...I love that 
> phrase, always makes me think of the cliff dwellings in the 
> southwest.)  802.11g just spreads the signal out across the entire set 
> of channels 802.11b uses... to get more bandwidth through. Someone 
> could have fired up an 802.11g system close-by if you live in an 
> apartment or tight quarters.  In that case, distance away from the 
> system is the best way to alleviate the problem.
>
> The joys of RF ... bit-rate is a linear math function to bandwidth.  To 
> get a higher bit-rate you have to up your bandwidth utilized.  However 
> RF signal decreases 2 X distance^2 as you move away from a 
> transmitter... an exponential function... so moving away from an 
> offending transmitter or noise source is usually more effective than 
> anything, especially at the low power levels allowed in 2.4 GHz devices.
>
> Of course... geeks constantly publish "hacks" to add external antennas 
> to 802.11b and other Part 15 devices.  Most of these are thankfully 
> very very bad designs (the infamous "Pringles Can" antennas come to 
> mind... complete crap from an RF design standpoint) and the geeks don't 
> feed them with hardline (coax is extremely lossy at 2.4 GHz... most of 
> your signal leave the coax and radiates or turns into heat before it 
> reaches the antenna) so they aren't very effective -- but some people 
> do figure out the "right" tools to use and exceed the Effective 
> Radiated Power (ERP) limits imposed by law on Part 15 devices by tens 
> to hundreds of watts, depending on the gain of their antenna system.  
> Luckily to get those levels of gain the signal has to be very 
> focused -- high gain antennas are very directional by design -- so the 
> interference problem is localized.
>
> The best advice for help:
>
> Experiment -- you should just try different channels until you find the 
> best performer.  Or a switch to 802.11a and move up a few GHz in 
> frequency would work too.  At least until those become popular.  ;-)  
> Once they all become overly-popular in a densely populated area -- 
> we're all basically hosed.  (GRIN)
>
> And the real reason for the problem:
>
> In general the FCC's stance right now is "give away bandwidth to 
> whoever wants it... and may the original licensees be damned."  This 
> shows clearly in the decisions made over the last five to ten years by 
> the Commission -- EXCEPT in the traditional broadcast bands.  Those are 
> locked up forever by the money and powerbase of the owners of the radio 
> and TV companies.
>
> Broadband-over-powerlines (or "BPL" as it's called) is turning into the 
> next huge RF battle.  BIG money behind it.  Huge interests who donate 
> to Congressional representatives and Senators.
>
> Most engineers agree, HF-band communications the world over will be 
> virtually wiped out by BPL technology -- it's been seen in the test 
> areas in the real world and also in the labs -- BPL noise will be 
> broadbanded and hideous.
>
> Ham Radio, Shortwave Broadcasts, and Emergency long-range 
> communications systems like FEMA and others have -- all will be 
> destroyed so people can have web pages and spam.  And yet, your elected 
> officials have appointed people to the FCC Commission Board (and this 
> is a direct quote from a Commissioner) who claim BPL is "Broadband 
> Nirvana."  Hmmm... another free-for-all coming, I think.
>
> Wonder who's paying them off... follow the money!  That's what good 
> investigators do...
>
> Sorry -- I wandered off-topic here, but anyway... that's where it's 
> headed... RF spectrum used to be completely unregulated, then 
> government stepped in, now government is backing out and going to let 
> "the markets" decide who uses what spectrum... at least over the 
> long-term that seems to be where it's all headed.  So like our legal 
> system -- your RF devices will work if you can afford the latest and 
> greatest gadgets with built in filtering for all the RF pollution 
> someday.  That level of RF pollution is coming -- probably sometime in 
> the next 30 years.
>
> Back to your issue:
>
> You'll probably have a hard time finding your noise source.  And 
> devices licensed under Part 15 of the FCC regulations and other 
> regulations like those that cover the ISM bands (Industrial, 
> Scientific, and Medical) like 2.4 GHz effectively wash clean the hands 
> of the only governing body capable of policing the RF spectrum.  It's 
> bad policy.  (900 MHz was the first to go... the licensed users of 900 
> MHz including Amateur Radio Operators and the Federal Government find 
> the band all but useless for many applications today because of baby 
> monitors, cordless phones, and other RF crud... oh yeah, I think 
> Ricochet is there too, and one other local wireless ISP -- Suburban 
> Broadband's gear.)
>
> Good luck with it... yes, 802.11b/g are a great application of 
> technology that has spurred on lots of business, but it comes at a 
> price... spectrum management is impossible on the 2.4 GHz bands now... 
> thus, certain limited incidents like yours where your device simply 
> won't work will happen more and more often.
>
> On the bright side, there's a big future in RF spectrum analysis 
> tools.  A friend works for a company that specializes in DSP-based 
> portable spectrum analysis gear.  So far the largest purchasers are 
> government agencies battling interference from commercial entities 
> (cell phone companies, some 2-way systems) who don't maintain their 
> licensed systems well -- but many investigations have led to 
> malfunctioning consumer gear.
>
> He related one story of asking a department store to turn off their 
> wireless music distribution system because the transmitter was 
> malfunctioning and jamming a local Police dispatch frequency.  And they 
> DIDN'T WANT TO.  They also attempted to turn it back on as soon as the 
> investigators went to leave, so they went in and just confiscated the 
> thing.  Great priorities, there guys... the customer MUST have 
> MUSAK!!!  Who cares if the cops can't talk on their radios?  ;-)
>
> Nate Duehr, nate at natetech.com
>
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