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Wireless-Friendly Microwaves
Makarand writes "According to this article on ABC News, scientists at the University of Michigan in Ann Arbor have stumbled upon a simple and elegant solution to keep your kitchen microwave from
becoming a noisy nuisance to your home Wi-Fi network.
They found that they could focus the microwaves into a single frequency and
reduce noisy
microwave emissions by placing ordinary magnets in specific patterns along the magnetron .
New techniques to reduce microwave interference will be needed when
Wi-Fi enabled entertainment systems will allow digital audio and video to be transmitted
to different rooms of a house wirelessly. Packet drops in such a sytem would degrade the video and audio
experience."
Cordless phones (not mobile) cause grief according to my colleagues.
Auto-check your UK lottery lines
Low-noise microwave magnetrons by azimuthally verying axial magnetic field - here
$ strings FTP.EXE | grep Copyright
@(#) Copyright (c) 1983 The Regents of the University of California.
The article stresses that those microwave interferences can be curtailed with "ordinary magnets" placed "in a specific pattern" so why isn't there a DIY guide for figuring out that pattern and slapping the magnets on the side of the oven? I know I'm probably oversimplifying, but if you know the pattern at which your oven emmits the microwaves, it can't be too hard to figure out the pattern at which you can put the magnets. Am I missing something? Or is it simply because, as they mentioned, reducing microwave interferences is a huge market and "opensourcing" the method would stop that?
I will continue to have the people in the appartment next door toasting my WiFi.
I have big problems with the radio that the CIA implanted in my brain.
The summary sez:"Packet drops in such a sytem would degrade the video and audio experience."
I'm much more concerned with interference from my WAN slowing down or altering the cooking time of my microwave!
Geek1: Hey guys, want some microwave popcorn?
Geeks: Sure!
Geek1: OK, turn off all the 802.11 stuff so it will cook.
I want to delete my account but Slashdot doesn't allow it.
They found that they could focus the microwaves into a single frequency
...
Why not go all the way and make the frequency and phase of the microwave oven's magnetron adjustable, add some kind of microcontroller to drive it, and a small cpu to implement the 802.11b stack. Then, from your laptop, run this script:
WIFI_IF=eth0
DATE=`date +%s`
while [ ! $TIMEOUT ];do
DATE_PREV=$DATE
tcpdump -i $WIFI_IF -c 1
DATE=`date +%s`
let TDIFF=DATE-DATE_PREV
if [ $TDIFF -gt 5 ];then
TIMEOUT=1
fi
done
echo "Coffee is hot!"
Ah, the marvels of technology
"A door is what a dog is perpetually on the wrong side of" - Ogden Nash
I'd be happy if my microwave just didn't whine and rattle because they didn't balance that turning thing
Think positive, this noise is actually a useful feature : when your oven becomes quiet, you know it's high time you cleaned the inside, because globules of sticky food are stuck in the rollers.
"A door is what a dog is perpetually on the wrong side of" - Ogden Nash
Nobody in their right mind would drink MICROWAVE COFFEE, right? Right??
But if you like it, you might as well boil your sport socks and underwear, add a dash of pergamot and enjoy a hot cup of "coffee".
If your microwave is interfering with any WiFi device not adjacent to it then throw it out and get a new one. Any properly shielded microwave should NOT be interfering with your WiFi signal. I worked for 2.5 years with the guys at Cisco/Aironet and we could only find one 15 year old off brand microwave that we could get to cause any noticable loss of signal in our testing shacks (basically an RF isolated chamber enclosed by a Faraday cage). None of the microwaves in the building ever caused us any problems even though we had more WiFi equipment than any place on earth. And if you don't want to/can't replace the microwave then get an 802.11a capable radio, different spectrum =)
There are 4 boxes to use in the defense of liberty: soap, ballot, jury, ammo. Use in that order. Starting now.
Microwaves DO interfere with WiFi. Case in point, when my wife is cooking here egg rolls in the microwave, my WiFi signal drops to zero. The microwave finishes and poof...11mb connections. If I can connect, I either get really really really SLOW connections, or I have to be ontop of the AP....literally! 2.4 GHz is what many call the garbage band...you got cordless phones, cellphones are close to it, microwaves, WiFi (both a and g), video units, intercoms, and just about anything you can think of all fighting for spectrum. 5GHz is going to be no better. I am waiting to see if the either start cleaning up 2.4 GHz which would be REALLY hard, or ramp up or down the frequency. I thing the 1.2 GHz ham band would be a good candidate for refarming. From Ham use, it's not even close to being useful for public service and even if there are radios, there's usually noone there even during rush hour. The range would be a bit better then 2.4Ghz and they could totally reserve it for WLANS of all types. As a ham, I am not usually in favor of killing a band (more in favor of addding ham bands), but almost no friends of mine work 1.2GHz and I am sure all of them would like a better WLAN connection! ;)
Gorkman
When you hit water with it, it will agitate the molecules and things get hot and cooked
You seem agitated and cooked enough without microwaves.
The difference is in power and concentration : a microwave oven is minimum 700W, concentrated on a lump of water, whereas an 802.11b is 100mW radiated in all directions. You'd need hundreds of wifi cards doing denial-of-services around a cage to even start incommodating the hamster inside.
"A door is what a dog is perpetually on the wrong side of" - Ogden Nash
Is the noise generated by an average microwave really that bad? Maybe it's just mine but it dosen't affect any of my wifi cards at all.
It does however manage to wipe out the video sender which runs on 2.4GHz aswell.
I am sitting here testing a forward error correcting file transfer protocol and in a fit of boredom I turn to Slashdot. This article is very timely as I needed a way of injecting some noise into the system.
Test environment:
IBM T-21 laptop with Orinoco gold 802.11b wireless PCCard.
SMC di-pole wireless AP (Forget the model number) which in testing has turned out to be a very good AP with range exceeding all of the standard 802.11b AP/routers we have tested.
The test file is 4MB in size and we are sending it in both directions across the wireless network with and without error correction. No suprises here, with a perfect signal the file with error correction takes slightly longer to arrive due to the increase in size. Transfer rate is about the equivalent speed to a network file copy and slightly faster than ftp on the same network.
After reading the article I moved the laptop to within two feet (as measured from microwave to the antenna of the access card) and re-ran the tests.
With the microwave off, all tests ran as normal, with the microwave on I get the following results.
Network file copy: Failed with network timeout, network not available
Our FEC file copy: completed but very slow
Our Non-FEC file copy: failed due to loss
Time to look closer. I fired up the Orinoco client tools for site monitoring which allow you to view various network conditions. With the network off the signal was typically at -72db and the noise was measured at -92db. With the microwave on the signal would range between -72db and -60db and noise would range from between -90db and -63db. With the microwave on the signal quality would range between non-existent and 'good'.
Running our tests produced the following results.
Microwave off:
-------- Transfer Summary --------
Data bytes: 45638341
Elapsed time: 91.93 seconds
Effective rate: 3971.44 Kbps
Packets lost: 11
Packets sent: 46853
Requested Rate: 10000
Actual Wire rate: 4370.70 Kbps
Average loss: 0.02%
Average RTT: 35.88 ms
Microwave on:
-------- Transfer Summary --------
Data bytes: 45638341
Elapsed time: 390.71 seconds
Effective rate: 934.47 Kbps
Packets lost: 3225
Packets sent: 50067
Requested Rate: 10000
Actual Wire rate: 1098.95 Kbps
Average loss: 6.44%
Average RTT: 85.03 ms
The two important numbers are effective wire rate and packets lost. Keep in mind that repeated attempts at shell based file copies failed completely as did a non-fec file copy using udp and tcp. This looks like a problem that really does need a solution, at least for 802.11b.
Oh, and my microwave is a two year old top of the line KitchenAid built in so it is surrounded by an additional metal frame and all of the wooden cabinets (and whatever they contain). Even with all that extra shielding it was massivly effecting the wireless throughput and presumably anything else within range, scary, I won't be standing too close to the microwave from now on when its on thats for sure.
2.4 GHz is not the resonating frequency of water. That's way way up in the GHz chain. 2.4 GHz was chosen because that band is the junk band in which unlicensed users are subject to interference as part of the spec.
Microwaves work by oscillating water molecules, which are dipole. The magnetron cycles 2.45 billions times per second, which twists the water molecules. The interior of a microwave oven is coated with a microwave-reflecting material which allows a single beam to essentially paint the three-dimensional interior.
So many people write that water resonates at 2.4 GHz. It's just not true. Here's a nice explanation of how it works.
Freelance tech journalist for the Economist, MIT Technology Review, Macworld, and others
I got extremely poor link quality from my 802.11b network - like, it would barely connect - until I tried changing the channel (from 3 to 12). This improved things enormously; I haven't tested all the channels to find the best one yet but it might be worth it if you're having problems, it definitely seems possible to get variations in signal quality within the 11b band.
"'I pass the test,' she said. 'I will diminish, and go into the West, and remain Galadriel.'"
- JRR Tolkien.
WiFi is an unlicensed, "Part 15" system. It has to accept all interference from all sources.
I'm not going to pay $2 more for a microwave just so people who can't figure out how to run ethernet can avoid dropped packets every time I warm up my cocoa.
JD
Every microwave I've ever taken apart just has the series of control parts (timer, switches, fuse) and the magnetron\waveguide assembly part of which is a feedhorn pointed directly into the cooking cavity.That's all it is. The metal chassis of the microwave reflects or grounds out the RF. The problem is not only does a microwave operate very,very close to the 2.5 gig band just like 802.11 spec it also has a crummy "see thru" screen on the front with holes punched out just slightly smaller than 1 or 2 mm. Just small enought to keep wavelengths around 10-12 centimeters and below inside the box and anything above that escapes. The magnetron is noisy, it emmits spurious rf across the spectrum. The FDA has emission standards for the later model ovens. 5 mWatt/sq.CM at any point within 10 CM of cooker! Most new microwaves do a lot better than that. Solution: obviously make better sheilding inside the box, maybe a wire webbing. (I wonder what's up with pacemakers?)
Relax, you're on our list for an upgrade. We're going to put the specially placed magnets around the transmitter. That should fix it.
Our grey alien friends should be around tonight to pick you up (if they anal-probe you, that wasn't our idea).
(The cup holder already works great)
No mod points, no meta-moderating/Firehose/all the other free work Slashdot wants me to do.
The paper said they used a DC power supply, and only speculates about what would happen with a real el-cheapo microwave oven power supply.
This matters because you can shift the frequency of a magnetron slightly off nominal resonance by varying the power input.
Microwave ovens ship with the crudest imaginable high-voltage source and the magnetron voltage isn't even approximately constant.
If the oven's frequency is bouncing around the spectrum, other users may not be able to stay out of the way.