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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
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?
More like be prepared to be booted as the microwave will cut off 802.11b. I did not have a problem with this until I bought my current microwave (it's a bit closer to the AP then the old one was). When ever the microwave is on, the signal drops to zilch and I disconnect. Makes me wonder how safe these things are! :)
Gorkman
Great - any idea how long these leaking microwaves have been inducing microtumors in my brain? How much longer until they grew large enough to kill me? Or how much longer until they just weird me out and I go all Charles Whitman-like on your ass?
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.
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.
As a ham who works satellites I would not just casually give away the 1.2 Ghz band. Rather, I would like to see WiFi move up to the 5 Ghz band rather than 1.2 Ghz. While I sort of agree that 1.2 Ghz is underutilized, 2.4 Ghz is where the primary downlink for AO-40 is located, and used worldwide. The 2.4 Ghz downlink suffers from interference by microwave ovens, and increasingly WiFi appliances, as well as other services near the band. 1.2 Ghz is a good frequency to uplink to the bird, if you have the equipment, though I agree with you that that 1.2 Ghz stations are hard to find and not easy or cheap to set up properly, due to high feedline losses, and lack of commercial equipment easily modifiable to work in the band.
On the other hand, the technology to clean up signals on microwave ovens could be a bonanza for those hams crazy enough to bounce signals off of the moon in the form of a cheap 500 watt transmitter on 2.4 Ghz. Finally moonbouncers will be able to get armchair copy of EME signals without having to visit Areceibo. I don't want to be in the line of fire of that signal though.
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?)
Just set "funny" to +3, all the rest to "-6" in Comment Options, and surf at +5 treshold. Will display only +3 Funny and above, discarding all otherwise moderated.
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How does water demodulate RF? To which mechanism are you referring?
/AC
And I thought I knew how inkjet priners work, but I fail to see the relveance to RF?
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.